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Number Won 2015. 7. 10. 23:54

July 10, 2015

NASA's Swift Reveals a Black Hole Bull's-eye

Rings of X-ray light centered on V404 Cygni, a binary system containing an erupting black hole (dot at center), were imaged by the X-ray Telescope aboard NASA's Swift satellite from June 30 to July 4. A narrow gap splits the middle ring in two. Color indicates the energy of the X-rays, with red representing the lowest (800 to 1,500 electron volts, eV), green for medium (1,500 to 2,500 eV), and the most energetic (2,500 to 5,000 eV) shown in blue. For comparison, visible light has energies ranging from about 2 to 3 eV. The dark lines running diagonally through the image are artifacts of the imaging system.

Credits: Andrew Beardmore (Univ. of Leicester) and NASA/Swift

Download frames from NASA Goddard's Scientific Visualization Studio

The Swift X-ray image of V404 Cygni covers a patch of the sky equal to about half the apparent diameter of the full moon. This image shows the rings as they appeared on June 30.

Credits: NASA's Scientific Visualization Studio (left), Andrew Beardmore (Univ. of Leicester); NASA/Swift (right)

What looks like a shooting target is actually an image of nested rings of X-ray light centered on an erupting black hole. on June 15, NASA's Swift satellite detected the start of a new outburst from V404 Cygni, where a black hole and a sun-like star orbit each other. Since then, astronomers around the world have been monitoring the ongoing light show.  

On June 30, a team led by Andrew Beardmore at the University of Leicester, U.K., imaged the system using the X-ray Telescope aboard Swift, revealing a series concentric rings extending about one-third the apparent size of a full moon. A movie made by combining additional observations acquired on July 2 and 4 shows the expansion and gradual fading of the rings.

Astronomers say the rings result from an "echo" of X-ray light. The black hole's flares emit X-rays in all directions. Dust layers reflect some of these X-rays back to us, but the light travels a longer distance and reaches us slightly later than light traveling a more direct path. The time delay creates the light echo, forming rings that expand with time.   

Detailed analysis of the expanding rings shows that they all originate from a large flare that occurred on June 26 at 1:40 p.m. EDT. There are multiple rings because there are multiple reflecting dust layers between 4,000 and 7,000 light-years away from us. Regular monitoring of the rings and how they change as the eruption continues will allow astronomers to better understand their nature.

"The flexible planning of Swift observations has given us the best dust-scattered X-ray ring images ever seen," Beardmore said. "With these observations we can make a detailed study of the normally invisible interstellar dust in the direction of this black hole."

V404 Cygni is located about 8,000 light-years away. Every couple of decades the black hole fires up in an outburst of high-energy light. Its previous eruption ended in 1989.

The investigating team includes scientists from the Universities of Leicester, Southampton, and Oxford in the U.K., the University of Alberta in Canada, and the European Space Agency in Spain.

Swift was launched in November 2004 and is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland. Goddard operates the spacecraft in collaboration with Penn State University in University Park, Pennsylvania, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Virginia. International collaborators are located in the United Kingdom and Italy. The mission includes contributions from Germany and Japan.

Related Links

·         NASA Missions Monitor a Waking Black Hole

·         INTEGRAL light curve of V404 Cygni

·         NASA’s Chandra Captures X-Ray Echoes Pinpointing Distant Neutron Star


Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Black Holes, Goddard Space Flight Center, Swift, Universe,

Black Holes

June 30, 2015

NASA Missions Monitor a Waking Black Hole

NASA's Swift satellite detected a rising tide of high-energy X-rays from the constellation Cygnus on June 15, just before 2:32 p.m. EDT. About 10 minutes later, the Japanese experiment on the International Space Station called the Monitor of All-sky X-ray Image (MAXI) also picked up the flare.

The outburst came from V404 Cygni, a binary system located about 8,000 light-years away that contains a black hole. Every couple of decades the black hole fires up in an outburst of high-energy light, becoming an X-ray nova. Until the Swift detection, it had been slumbering since 1989.

On June 15, NASA's Swift caught the onset of a rare X-ray outburst from a stellar-mass black hole in the binary system V404 Cygni. Astronomers around the world are watching the event. In this system, illustrated in this animation, a stream of gas from a star much like the sun flows toward a 10 solar mass black hole. Instead of spiraling toward the black hole, the gas accumulates in an accretion disk around it. Every couple of decades, the disk switches into a state that sends the gas rushing inward, starting a new outburst.

Credits: NASA's Goddard Space Flight Center

Download this video in HD formats from NASA Goddard's Scientific Visualization Studio http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=11110

An X-ray nova is a bright, short-lived X-ray source that reaches peak intensity in a few days and then fades out over a period of weeks or months. The outburst occurs when stored gas abruptly rushes toward a neutron star or black hole. By studying the patterns of the X-rays produced, astronomers can determine the kind of object at the heart of the eruption.

"Relative to the lifetime of space observatories, these black hole eruptions are quite rare," said Neil Gehrels, Swift's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "So when we see one of them flare up, we try to throw everything we have at it, monitoring across the spectrum, from radio waves to gamma rays."

Astronomers classify this type of system as a low-mass X-ray binary. In V404 Cygni, a star slightly smaller than the sun orbits a black hole 10 times its mass in only 6.5 days. The close orbit and strong gravity of the black hole produce tidal forces that pull a stream of gas from its partner. The gas travels to a storage disk around the black hole and heats up to millions of degrees, producing a steady stream of X-rays as it falls inward.

But the disk flips between two dramatically different conditions. In its cooler state, the gas resists inward flow and just collects in the outer part of the disk like water behind a dam. Inevitably the build-up of gas overwhelms the dam, and a tsunami of hot bright gas rushes toward the black hole.

Astronomers relish the opportunity to collect simultaneous multiwavelength data on black hole binaries, especially one as close as V404 Cygni. In 1938 and 1956, astronomers caught V404 Cygni undergoing outbursts in visible light. During its eruption in 1989, the system was observed by Ginga, an X-ray satellite operated by Japan, and instruments aboard Russia's Mir space station.

"Right now, V404 Cygni shows exceptional variation at all wavelengths, offering us a rare chance to add to this unique data set," said Eleonora Troja, a Swift team member at Goddard.

Ongoing or planned satellite observations of the outburst involve NASA’s Swift satellite, Chandra X-ray Observatory and Fermi Gamma-ray Space Telescope, as well as Japan’s MAXI, the European Space Agency's INTEGRAL satellite, and the Italian Space Agency's AGILE gamma-ray mission. Ground-based facilities following the eruption include the 10.4-meter Gran Telescopio Canarias operated by Spain in the Canary Islands, the University of Leicester's 0.5-meter telescope in Oadby, U.K., the Nasu radio telescope at Waseda University in Japan, and amateur observatories.

V404 Cygni has flared many times since the eruption began, with activity ranging from minutes to hours. "It repeatedly becomes the brightest object in the X-ray sky -- up to 50 times brighter than the Crab Nebula, which is normally one of the brightest sources," said Erik Kuulkers, the INTEGRAL project scientist at ESA's European Space Astronomy Centre in Madrid. "It is definitely a 'once in a professional lifetime' opportunity."

In a single week, flares from V404 Cygni generated more than 70 "triggers" of the Gamma-ray Burst Monitor (GBM) aboard Fermi. This is more than five times the number of triggers seen from all objects in the sky in a typical week. The GBM triggers when it detects a gamma-ray flare, then it sends numerous emails containing increasingly refined information about the event to scientists on duty.

Every time the GBM recovered from one trigger, V404 Cygni set it off again, resulting in a torrent of emails. The event prompted David Yu, a GBM scientist at the Max Planck Institute of Extraterrestrial Physics in Garching, Germany, to comment on social media: "Achievement Unlocked: Mailbox spammed by a blackhole."

Related Links

Swift detects the V404 Cygni outburst
http://gcn.gsfc.nasa.gov/gcn/gcn3/17929.gcn3

Alert notice from the American Association of Variable Star Observers
www.aavso.org/aavso-alert-notice-520

NASA's Swift Satellite Discovers a New Black Hole in our Galaxy
www.nasa.gov/mission_pages/swift/bursts/new-black-hole.html

Francis Reddy

NASA's Goddard Space Flight Center, Greenbelt, Maryland

Last Updated: July 10, 2015

Editor: Karl Hille

Tags:  Black Holes, Chandra X-Ray Observatory, Fermi Gamma-Ray Space Telescope, Goddard Space Flight Center, Swift, Universe,

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Dark Energy/Matter

June 24, 2015

NASA Simulation Suggests Black Holes May Make Ideal Dark Matter Labs

A new NASA computer simulation shows that dark matter particles colliding in the extreme gravity of a black hole can produce strong, potentially observable gamma-ray light. Detecting this emission would provide astronomers with a new tool for understanding both black holes and the nature of dark matter, an elusive substance accounting for most of the mass of the universe that neither reflects, absorbs nor emits light.

"While we don't yet know what dark matter is, we do know it interacts with the rest of the universe through gravity, which means it must accumulate around supermassive black holes," said Jeremy Schnittman, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "A black hole not only naturally concentrates dark matter particles, its gravitational force amplifies the energy and number of collisions that may produce gamma rays."

A new computer simulation explores the connection between two of the most elusive phenomena in the universe, black holes and dark matter. Download this video in HD formats from NASA Goddard's Scientific Visualization Studio http://svs.gsfc.nasa.gov/goto?11894

Credits: NASA's Goddard Space Flight Center

In a study published in The Astrophysical Journal on June 23, Schnittman describes the results of a computer simulation he developed to follow the orbits of hundreds of millions of dark matter particles, as well as the gamma rays produced when they collide, in the vicinity of a black hole. He found that some gamma rays escaped with energies far exceeding what had been previously regarded as theoretical limits.

In the simulation, dark matter takes the form of Weakly Interacting Massive Particles, or WIMPS, now widely regarded as the leading candidate of what dark matter could be. In this model, WIMPs that crash into other WIMPs mutually annihilate and convert into gamma rays, the most energetic form of light. But these collisions are extremely rare under normal circumstances.

Over the past few years, theorists have turned to black holes as dark matter concentrators, where WIMPs can be forced together in a way that increases both the rate and energies of collisions. The concept is a variant of the Penrose process, first identified in 1969 by British astrophysicist Sir Roger Penrose as a mechanism for extracting energy from a spinning black hole. The faster it spins, the greater the potential energy gain.

Show only LeftShow only Right

A new computer simulation reveals that dark matter particles orbiting a black hole produce a strong and potentially detectable signal of high-energy gamma rays. Left: This visualization shows dark matter particles as gray spheres attached to shaded trails representing their motion. Redder trails indicate particles more strongly affected by the black hole's gravitation and closer to its event horizon (black sphere at center, mostly hidden by trails). The ergosphere, where all matter and light must follow the black hole's spin, is shown in teal. The black hole is viewed along its equator and rotates left to right. Right: This image shows the gamma-ray signal produced in the computer simulation by annihilations of dark matter particles. Lighter colors indicate higher energies, with the highest-energy gamma rays originating from the center of the crescent-shaped region at left, closest to the black hole's equator and event horizon. The gamma rays with the greatest chances of escape are produced on the side of the black hole that spins toward us. Such lopsided emission is typical for a rotating black hole.

Credits: NASA Goddard's Space Flight Center Scientific Visualization Studio (left) and NASA Goddard/Jeremy Schnittman

In this process, all of the action takes place outside the black hole's event horizon, the boundary beyond which nothing can escape, in a flattened region called the ergosphere. Within the ergosphere, the black hole's rotation drags space-time along with it and everything is forced to move in the same direction at nearly speed of light. This creates a natural laboratory more extreme than any possible on Earth.

The faster the black hole spins, the larger its ergosphere becomes, which allows high-energy collisions further from the event horizon. This improves the chances that any gamma rays produced will escape the black hole.  

"Previous work indicated that the maximum output energy from the collisional version of the Penrose process was only about 30 percent higher than what you start with,"  Schnittman said. In addition, only a small portion of high-energy gamma rays managed to escape the ergosphere. These results suggested that clear evidence of the Penrose process might never be seen from a supermassive black hole.

But the earlier studies included simplifying assumptions about where the highest-energy collisions were most likely to occur. Moving beyond this initial work meant developing a more complete computational model, one that tracked large numbers of particles as they gathered near a spinning black hole and interacted among themselves.

Schnittman's computer simulation does just that. By tracking the positions and properties of hundreds of millions of randomly distributed particles as they collide and annihilate each other near a black hole, the new model reveals processes that produce gamma rays with much higher energies, as well as a better likelihood of escape and detection, than ever thought possible. He identified previously unrecognized paths where collisions produce gamma rays with a peak energy 14 times higher than that of the original particles.

Using the results of this new calculation, Schnittman created a simulated image of the gamma-ray glow as seen by a distant observer looking along the black hole's equator. The highest-energy light arises from the center of a crescent-shaped region on the side of the black hole spinning toward us. This is the region where gamma rays have the greatest chance of exiting the ergosphere and being detected by a telescope.

The research is the beginning of a journey Schnittman hopes will one day culminate with the incontrovertible detection of an annihilation signal from dark matter around a supermassive black hole.

"The simulation tells us there is an astrophysically interesting signal we have the potential of detecting in the not too distant future, as gamma-ray telescopes improve," Schnittman said. "The next step is to create a framework where existing and future gamma-ray observations can be used to fine-tune both the particle physics and our models of black holes."

Related links:

Download high-resolution images and video in HD formats from NASA Goddard's Scientific Visualization Studio

svs.gsfc.nasa.gov/goto?11894 

Paper: The Distribution and Annihilation of Dark Matter Around Black Holes

http://iopscience.iop.org/0004-637X/806/2/264

Paper: Revised Upper Limit to Energy Extraction from a Kerr Black Hole

dx.doi.org/10.1103/PhysRevLett.113.261102

NASA-Led Study Explains Decades of Black Hole Observations

www.nasa.gov/topics/universe/features/black-hole-study.html

Francis Reddy
NASA's Goddard Space Flight Center
, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Karl Hille

Tags:  Black Holes, Dark Energy and Dark Matter, Fermi Gamma-Ray Space Telescope, Goddard Space Flight Center, Universe,

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Hubble

June 19, 2015

NASA’s Hubble Sees the 'Teenage Years' of Quasars

What was happening in the universe 12 billion years ago? The universe was smaller and so crowded that galaxies collided with each other much more frequently than today. Hubble astronomers looked at dusty quasars where their glow was suppressed by dust, allowing a view of the quasar's surroundings.

Credits: NASA/ESA

Astronomers have used the Hubble Space Telescope’s infrared vision to uncover the mysterious early formative years of quasars, the brightest objects in the universe. Hubble’s sharp images unveil chaotic collisions of galaxies that fuel quasars by feeding supermassive central black holes with gas.

“The Hubble observations are definitely telling us that the peak of quasar activity in the early universe is driven by galaxies colliding and then merging together,” said Eilat Glikman of Middlebury College in Vermont. “We are seeing the quasars in their teenage years, when they are growing quickly and all messed up.”

Discovered in the 1960s, a quasar, contraction of “quasi-stellar object,” pours out the light of as much as one trillion stars from a region of space smaller than our solar system. It took more than two decades of research to come to the conclusion that the source of the light is a gusher of energy coming from supermassive black holes inside the cores of very distant galaxies.

The lingering question has been what turns these brilliant beacons on, and now Hubble has provided the best solution. “The new images capture the transitional phase in the merger-driven black hole scenario,” Glikman said. “The Hubble images are incredibly beautiful.”

“We’ve been trying to understand why galaxies start feeding their central black holes, and galaxy collisions are one leading hypothesis. These observations show that the brightest quasars in the universe really do live in merging galaxies,” said co-investigator Kevin Schawinski of the Swiss Federal Institute of Technology Zurich.

The overwhelming glow of the quasar drowns out the light of the accompanying galaxy, making the signs of mergers difficult to see. Glikman came up with a clever way to use Hubble’s sensitivity at near-infrared wavelengths of light to see the host galaxies by aiming at quasars that are heavily shrouded in dust. The dust dims the quasar’s visible light so that the underlying galaxy can be seen.

The gravitational forces of the merger rob much of the angular momentum that keeps gas suspended in the disks of the colliding galaxies. As galaxies merge, gravitational forces cause the gas in the disks of the colliding galaxies to fall directly toward the supermassive black hole. The accretion zone around the black hole is so engorged with fuel it converts it into a gusher of radiation that blazes across the universe.

Glikman looked for candidate “dust-reddened quasars” in several ground-based infrared and radio sky surveys. Active galaxies in this early phase of evolution are predicted to glow brightly across the entire electromagnetic spectrum, making them detectable in radio and near-infrared wavelengths that are not as easily obscured as other radiation.

She then used Hubble’s Wide Field Camera 3 to take a detailed look at the best candidate targets. Glikman looked at the dust-reddened light of 11 ultra-bright quasars that exist at the peak of the universe’s star-formation era, which was 12 billion years ago. The infrared capability of Hubble’s Wide Field Camera 3 was able to probe deep into the birth of this quasar era.

The paper will be published in the June 18 issue of the Astrophysical Journal.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

For more images and information about the Hubble Space Telescope, visit: http://hubblesite.org/news/2015/20  and http://www.nasa.gov/hubble

Felicia Chou
Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Last Updated: July 10, 2015

Editor: Lynn Jenner

Tags:  Black Holes, Dark Energy and Dark Matter, Galaxies, Goddard Space Flight Center, Hubble Space Telescope, Stars, Universe,

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Black Holes

May 29, 2015

Large Hubble Survey Confirms Link between Mergers and Supermassive Black Holes with Relativistic Jets

A team of astronomers using the Hubble Space Telescope found an unambiguous link between the presence of supermassive black holes that power high-speed, radio-signal-emitting jets and the merger history of their host galaxies. Almost all galaxies with the jets were found to be merging with another galaxy, or to have done so recently.

The team studied a large selection of galaxies with extremely luminous centers — known as active galactic nuclei — thought to be the result of large quantities of heated matter circling around and being consumed by a supermassive black hole. While most galaxies are thought to host supermassive black holes, only a small percentage of them are this luminous and fewer still go one step further and form what are known as relativistic jets. The two high-speed jets of plasma move almost at the speed of light and stream out in opposite directions at right angles to the disc of matter surrounding the black hole, extending thousands of light-years into space.

Future observations could expand the survey set even further and continue to shed light on these complex and powerful processes.

For full story:

https://www.spacetelescope.org/news/heic1511/  

Image credit: NASA/ESA/STScI
Text credit: European Space Agency

Last Updated: July 10, 2015

Editor: Ashley Morrow

Tags:  Black Holes, Galaxies, Goddard Space Flight Center, Hubble Space Telescope, Universe,

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Hubble

May 28, 2015

Hubble Video Shows Shock Collision inside Black Hole Jet

When you’re blasting though space at more than 98 percent of the speed of light, you may need driver’s insurance. Astronomers have discovered for the first time a rear-end collision between two high-speed knots of ejected matter. This discovery was made while piecing together a time-lapse movie of a plasma jet blasted from a supermassive black hole inside a galaxy located 260 million light-years from earth.

The finding offers new insights into the behavior of “light saber-like” jets that are so energized that they appear to zoom out of black hole at speeds several times the speed of light. This “superluminal” motion is an optical illusion due to their being pointed very close to our line of sight and very fast speeds.

This time-lapse movie of an extragalactic jet was assembled from 20 years of Hubble Space Telescope observations of the core of the elliptical galaxy NGC 3862.

Credits: NASA, ESA, and E. Meyer STScI

Such extragalactic jets are not well understood. They appear to transport energetic plasma in a confined beam from the active nucleus of the host galaxy. The new analysis suggests that shocks produced by collisions within the jet further accelerate particles and brighten the regions of colliding material.    

The video of the jet was assembled with two decades’ worth of NASA Hubble Space Telescope images of the elliptical galaxy NGC 3862, the sixth brightest galaxy and one of only a few active galaxies with jets seen in visible light. The jet was discovered in optical light by Hubble in 1992. NGC 3862 is in a rich cluster of galaxies known as Abell 1367, located in the constellation Leo.

In the central region of galaxy NGC 3862 an extragalactic jet of material can be seen at the 3 o'clock position (left). Hubble images (right) of knots (outlined in red, green and blue) shows them moving along the jet over 20 years. The "X" is the black hole.

Credits: NASA, ESA, and E. Meyer STScI

The jet from NGC 3862 has a string-of-pearls structure of glowing knots of material. Taking advantage of Hubble's sharp resolution and long-term optical stability, Eileen Meyer of the Space Telescope Science Institute (STScI) in Baltimore, Maryland assembled a video from archival data to better understand jet motions. Meyer was surprised to see a fast knot with an apparent speed of seven times the speed of light catch up with the end of a slower moving, but still superluminal, knot along the string.

The resulting “shock collision” caused the merging blobs to brighten significantly.

“Something like this has never been seen before in an extragalactic jet,” said Meyer. As the knots continue merging they will brighten further in the coming decades. “This will allow us a very rare opportunity to see how the energy of the collision is dissipated into radiation.”

It’s not uncommon to see knots of material in jets ejected from gravitationally compact objects, but it is rare that motions have been observed with optical telescopes, and so far out from the black hole, thousands of light-years away. In addition to black holes, newly forming stars eject narrowly collimated streamers of gas that have a knotty structure. one theory is that material falling onto the central object is superheated and ejected along the object’s spin axis. Powerful magnetic fields constrain the material into a narrow jet. If the flow of the infalling material is not smooth, blobs are ejected like a string of cannon balls rather than a steady hose-like flow.

Whatever the mechanism, the fast-moving knot will burrow its way out into intergalactic space. A knot launched later, behind the first one, may have less drag from the shoveled-out interstellar medium and catch up to the earlier knot, rear-ending it in a shock collision.

Beyond the collision, which will play out over the next few decades, this discovery marks only the second case of superluminal motion measured at hundreds to thousands of light-years from the black hole where the jet was launched. This indicates that the jets are still very, very close to the speed of light even on distances that start to rival the scale of the host galaxy. These measurements can give insights into how much energy jets carry out into their host galaxy and beyond, which is important for understanding how galaxies evolve as the universe ages.

Meyer is currently making a Hubble-image video of two more jets in the nearby universe, to look for similar fast motions. She notes that these kinds of studies are only possible because of the long operating lifetime of Hubble, which has now been looking at some of these jets for over 20 years.

Extragalactic jets have been detected at X-ray and radio wavelengths in many active galaxies powered by central black holes, but only a few have been seen in optical light. Astronomers do not yet understand why some jets are seen in visible light and others are not.

Meyer’s results are being reported in the May 28 issue of the journal Nature.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. STScI conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

For images and more information about the Hubble Space Telescope, visit:

http://www.nasa.gov/hubble
http://hubblesite.org/news/2015/19

Felicia Chou
NASA Headquarters, Washington
202-358-0257
felicia.chou@nasa.gov

Ray Villard
Space Telescope Science Institute, Baltimore
410-338-4514
villard@stsci.edu

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Black Holes, Goddard Space Flight Center, Hubble Space Telescope, Universe,

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Kepler and K2

May 21, 2015

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NASA Spacecraft Capture Rare, Early Moments of Baby Supernovae

Astronomers are going gaga over newborn supernova measurements taken by NASA’s Kepler and Swift spacecraft, poring over them in hopes of better understanding what sparks these world-shattering stellar explosions. Scientists are particularly fascinated with Type la supernovae, as they can serve as a lighthouse for measuring the vast distances across space.

“Kepler’s unprecedented pre-event supernova observations and Swift’s agility in responding to supernova events have both produced important discoveries at the same time but at very different wavelengths,” says Paul Hertz, Director of Astrophysics. “Not only do we get insight into what triggers a Type Ia supernova, but these data allow us to better calibrate Type Ia supernovae as standard candles, and that has implications for our ability to eventually understand the mysteries of dark energy.”

The graphic depicts a light curve of the newly discovered Type Ia supernova, KSN 2011b, from NASA's Kepler spacecraft. The light curve shows a star's brightness (vertical axis) as a function of time (horizontal axis) before, during and after the star exploded. The white diagram on the right represents 40 days of continuous observations by Kepler. In the red zoom box, the agua-colored region is the expected 'bump' in the data if a companion star is present during a supernova. The measurements remained constant (yellow line) concluding the cause to be the merger of two closely orbiting stars, most likely two white dwarfs. The finding provides the first direct measurements capable of informing scientists of the cause of the blast.

Credits: NASA Ames/W. Stenzel

Type Ia supernovae explode with similar brightness because the exploding object is always a white dwarf, the Earth-sized remnant of a star like the sun. A white dwarf can go supernova by merging with another white dwarf or by pulling too much matter from a nearby companion star, causing a thermonuclear reaction and blowing itself to smithereens.

In studies appearing in Nature on Thursday, Kepler and Swift have found supporting evidence for both star-pulverizing scenarios.

Researchers studying the Kepler data have caught three new and distant supernovae, and the dataset includes measurements taken before the violent explosions even happened. Known for its planet-hunting prowess and its unceasing gaze, the Kepler space telescope's exquisitely precise and frequent observations every 30 minutes have allowed astronomers to turn back the clock and dissect the initial moments of a supernova. The finding provides the first direct measurements capable of informing scientists of the cause of the blast.

"Our Kepler supernova discoveries strongly favor the white dwarf merger scenario, while the Swift study, led by Cao, proves that Type Ia supernovae can also arise from single white dwarfs," said Robert Olling, research associate at the University of Maryland and lead author of the study. "Just as many roads lead to Rome, nature may have several ways to explode white dwarf stars."

To capture the earliest moments of Type Ia explosions, the research team monitored 400 galaxies for two years using Kepler. The team discovered three events, designated KSN 2011b, KSN 2011c and KSN 2012a, with measurements taken before, during and after the explosions.

These early data provide a view into the physical processes that ignite these stellar bombs hundreds of millions of light years away. When a star goes supernova, the explosive burst of energy ejects the star's material at hypersonic velocity, emitting a shock wave in all directions. If a companion star is in the neighborhood, the disruption in the shock wave will be recorded in the data.

Scientists found no evidence of a companion star and concluded the cause to be the collision and merger of two closely orbiting stars, most likely two white dwarfs.

Knowing the distance to a galaxy in the Kepler survey was key to characterizing the type of supernova uncovered by Olling and his colleagues. To determine the distance, the team turned to the powerful telescopes at the Gemini and the W. M. Keck Observatories atop Mauna Kea in Hawaii. These measurements were key for the researchers to conclude that the supernovae they had discovered were that of the Type Ia lighthouse variety.

“The Kepler spacecraft has delivered yet another surprise, playing an unexpected role in supernova science by providing the first well-sampled early time light curves of Type Ia supernovae," said Steve Howell, Kepler project scientist at NASA's Ames Research Center in Moffett Field, California. "Now in its new mission as K2, the spacecraft will search for more supernovae among many thousands of galaxies."

This computer simulation shows the debris of a Type Ia supernova (brown) slamming into its companion star (blue) at tens of millions of miles per hour. The interaction produces ultraviolet light that escapes as the supernova shell sweeps over the companion, a signal detected by Swift.

Credits: UC Berkeley, Daniel Kasen

A separate group of astronomers have also found intriguing data on a different supernova. Led by California Institute of Technology (Caltech) graduate student Yi Cao, a team using Swift has detected an unprecedented flash of ultraviolet (UV) light in the first few days of a Type Ia supernova. Based on computer simulations of supernovae exploding in binary star systems, the researchers think the UV pulse was emitted when the supernova’s blast wave slammed into and engulfed a nearby companion star.  

"If Swift had looked just a day or two later, we would have missed the prompt UV flash entirely," said Brad Cenko, a Swift team member at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Thanks to Swift's wavelength coverage and rapid scheduling capability, it is currently the only spacecraft that can regularly make these observations."

According to the analysis, the supernova debris slammed into and swept around its companion star, creating a region of UV emission. The peak temperature exceeded 19,000 degrees Fahrenheit (11,000 degrees Celsius) or about twice the surface temperature of the sun.  

The explosion, designated iPTF14atg, was first seen on May 3, 2014, in the galaxy IC 831, located about 300 million light-years away in the constellation Coma Berenices. It was discovered through a wide-field robotic observing system known as the intermediate Palomar Transient Factory (iPTF), a multi-institute collaboration led by the Caltech Optical Observatories in California.

"We saw no evidence of this explosion in images taken the previous night, so we found iPTF14atg when it was only about one day old," Cao said. "Better yet, we confirmed it was a young Type Ia supernova, something we've worked hard designing our system to find."

The team immediately requested follow-up observations from other facilities, including ultraviolet and X-ray observations from NASA's Swift satellite. Although no X-rays were found, a fading spike of UV light was caught by Swift's Ultraviolet/Optical Telescope within a few days of the explosion, with no corresponding spike at visible wavelengths. After the flash faded, both UV and visible wavelengths rose together as the supernova brightened.

The UV pulse from iPTF14atg provides strong evidence for the presence of a companion star, but as white dwarfs crashing into each other can also produce supernovae, as demonstrated by the Kepler results, astronomers are working to determine the percentage of supernovae produced by each one.

The scientists add that a better understanding of the differences among Type Ia explosions will help astronomers improve their knowledge of dark energy, a mysterious force that appears to be accelerating cosmic expansion.  

Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corp. operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

Swift blasted into orbit Nov. 20, 2004. Managed by Goddard, the mission is operated in collaboration with Penn State University in University Park, Pennsylvania, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy, with additional collaborators in Germany and Japan.

Animation showing a binary star system in which a white dwarf accretes matter from a normal companion star. Matter streaming from the red star accumulates on the white dwarf until the dwarf explodes. With its partner destroyed, the normal star careens into space. This scenario results in what astronomers refer to as a Type Ia supernova.

Credits: NASA's Goddard Space Flight Center/Walt Feimer


Michele Johnson
NASA’s Ames Research Center, Moffett Field, Calif.
650-604-6982
michele.johnson@nasa.gov

Lynn Chandler
NASA’s Goddard Space Flight Center, Greenbelt, Md.
301-286-2806
lynn.chandler-1@nasa.gov 

Last Updated: July 10, 2015

Editor: Michele Johnson

Tags:  Ames Research Center, Goddard Space Flight Center, Kepler and K2, Supernova, Swift, Universe,

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Stars

Jan. 6, 2015

NASA Observatories Take an Unprecedented Look into Superstar Eta Carinae

Eta Carinae, the most luminous and massive stellar system within 10,000 light-years of Earth, is known for its surprising behavior, erupting twice in the 19th century for reasons scientists still don't understand. A long-term study led by astronomers at NASA's Goddard Space Flight Center in Greenbelt, Maryland, used NASA satellites, ground-based telescopes and theoretical modeling to produce the most comprehensive picture of Eta Carinae to date. New findings include Hubble Space Telescope images that show decade-old shells of ionized gas racing away from the largest star at a million miles an hour, and new 3-D models that reveal never-before-seen features of the stars' interactions.

"We are coming to understand the present state and complex environment of this remarkable object, but we have a long way to go to explain Eta Carinae's past eruptions or to predict its future behavior," said Goddard astrophysicist Ted Gull, who coordinates a research group that has monitored the star for more than a decade.

Located about 7,500 light-years away in the southern constellation of Carina, Eta Carinae comprises two massive stars whose eccentric orbits bring them unusually close every 5.5 years. Both produce powerful gaseous outflows called stellar winds, which enshroud the stars and stymy efforts to directly measure their properties. Astronomers have established that the brighter, cooler primary star has about 90 times the mass of the sun and outshines it by 5 million times. While the properties of its smaller, hotter companion are more contested, Gull and his colleagues think the star has about 30 solar masses and emits a million times the sun's light.

Explore Eta Carinae from the inside-out with the help of supercomputer simulations and data from NASA satellites and ground-based observatories.

Credits: NASA's Goddard Space Flight Center

Download this video and additional multimedia in HD formats from NASA Goddard's Scientific Visualization Studio

Speaking at a press conference at the American Astronomical Society meeting in Seattle on Wednesday, the Goddard researchers discussed recent observations of Eta Carinae and how they fit with the group's current understanding of the system.

At closest approach, or periastron, the stars are 140 million miles (225 million kilometers) apart, or about the average distance between Mars and the sun. Astronomers observe dramatic changes in the system during the months before and after periastron. These include X-ray flares, followed by a sudden decline and eventual recovery of X-ray emission; the disappearance and re-emergence of structures near the stars detected at specific wavelengths of visible light; and even a play of light and shadow as the smaller star swings around the primary.

During the past 11 years, spanning three periastron passages, the Goddard group has developed a model based on routine observations of the stars using ground-based telescopes and multiple NASA satellites. "We used past observations to construct a computer simulation, which helped us predict what we would see during the next cycle, and then we feed new observations back into the model to further refine it," said Thomas Madura, a NASA Postdoctoral Program Fellow at Goddard and a theorist on the Eta Carinae team.

Seen in blue light emitted by doubly ionized iron atoms (4,659 angstroms), these images of Eta Carinae were captured by Hubble's STIS instrument between 2010 and 2014. Gas shells created during the binary's 2003 close approach race outward at about 1 million mph (1.6 million km/h).

Credits: NASA's Goddard Space Flight Center/T. Gull et al.

In this supercomputer simulation, the stars of Eta Carinae are shown as black dots. Lighter colors indicate greater densities in the stellar winds produced by each star. At closest approach, the fast wind of the smaller star carves a tunnel in the thicker wind of the larger star.

Credits: NASA's Goddard Space Flight Center/T. Madura

Eta Carinae's great eruption in the 1840s created the billowing Homunculus Nebula, imaged here by Hubble. Now about a light-year long, the expanding cloud contains enough material to make at least 10 copies of our sun. Astronomers cannot yet explain what caused this eruption.

Credits: NASA, ESA, and the Hubble SM4 ERO Team

According to this model, the interaction of the two stellar winds accounts for many of the periodic changes observed in the system. The winds from each star have markedly different properties: thick and slow for the primary, lean and fast for the hotter companion. The primary's wind blows at nearly 1 million mph and is especially dense, carrying away the equivalent mass of our sun every thousand years. By contrast, the companion's wind carries off about 100 times less material than the primary's, but it races outward as much as six times faster.

Madura's simulations, which were performed on the Pleiades supercomputer at NASA's Ames Research Center in Moffett Field, California, reveal the complexity of the wind interaction. When the companion star rapidly swings around the primary, its faster wind carves out a spiral cavity in the dense outflow of the larger star. To better visualize this interaction, Madura converted the computer simulations to 3-D digital models and made solid versions using a consumer-grade 3-D printer. This process revealed lengthy spine-like protrusions in the gas flow along the edges of the cavity, features that hadn't been noticed before.    

"We think these structures are real and that they form as a result of instabilities in the flow in the months around closest approach," Madura said. "I wanted to make 3-D prints of the simulations to better visualize them, which turned out to be far more successful than I ever imagined." A paper detailing this research has been submitted to the journal Monthly Notices of the Royal Astronomical Society.

The team detailed a few key observations that expose some of the system's inner workings. For the past three periastron passages, ground-based telescopes in Brazil, Chile, Australia and New Zealand have monitored a single wavelength of blue light emitted by helium atoms that have lost a single electron. According to the model, the helium emission tracks conditions in the primary star's wind. The Space Telescope Imaging Spectrograph (STIS) aboard Hubble captures a different wavelength of blue light emitted by iron atoms that have lost two electrons, which uniquely reveals where gas from the primary star is set aglow by the intense ultraviolet light of its companion. Lastly, X-rays from the system carry information directly from the wind collision zone, where the opposing winds create shock waves that heat the gas to hundreds of millions of degrees.

"Changes in the X-rays are a direct probe of the collision zone and reflect changes in how these stars lose mass," said Michael Corcoran, an astrophysicist with the Universities Space Research Association headquartered in Columbia, Maryland. He and his colleagues compared periastron emission measured over the past 20 years by NASA's Rossi X-ray Timing Explorer, which ceased operation in 2012, and the X-ray Telescope aboard NASA's Swift satellite. In July 2014, as the stars rushed toward each other, Swift observed a series of flares culminating in the brightest X-ray emission yet seen from Eta Carinae. This implies a change in mass loss by one of the stars, but X-rays alone cannot determine which one.

Goddard's Mairan Teodoro led the ground-based campaign tracking the helium emission. "The 2014 emission is nearly identical to what we saw at the previous periastron in 2009, which suggests the primary wind has been constant and that the companion's wind is responsible for the X-ray flares," he explained.

After NASA astronauts repaired the Hubble Space Telescope's STIS instrument in 2009, Gull and his collaborators requested to use it to observe Eta Carinae. By separating the stars' light into a rainbow-like spectrum, STIS reveals the chemical make-up of their environment. But the spectrum also showed wispy structures near the stars that suggested the instrument could be used to map a region close to the binary system in never-before-seen detail.

STIS views its targets through a single narrow slit to limit contamination from other sources. Since December 2010, Gull's team has regularly mapped a region centered on the binary by capturing spectra at 41 different locations, an effort similar to building up a panoramic picture from a series of snapshots. The view spans about 430 billion miles (670 billion km), or about 4,600 times the average Earth-sun distance.

The resulting images, revealed for the first time on Wednesday, show that the doubly ionized iron emission comes from a complex gaseous structure nearly a tenth of a light-year across, which Gull likens to Maryland blue crab. By stepping through the STIS images, vast shells of gas representing the crab's "claws" can be seen racing away from the stars with measured speeds of about 1 million mph (1.6 million km/h). With each close approach, a spiral cavity forms in the larger star's wind and then expands outward along with it, creating the moving shells.

"These gas shells persist over thousands of times the distance between Earth and the sun," Gull explained. "Backtracking them, we find the shells began moving away from the primary star about 11 years or three periastron passages ago, providing us with an additional way to glimpse what occurred in the recent past."

When the stars approach, the companion becomes immersed in the thickest part of the primary's wind, which absorbs its UV light and prevents the radiation from reaching the distant gas shells. Without this energy to excite it, the doubly ionized iron stops emitting light and the crab structure disappears at this wavelength. once the companion swings around the primary and clears the densest wind, its UV light escapes, re-energizes iron atoms in the shells, and the crab returns. 

Both of the massive stars of Eta Carinae may one day end their lives in supernova explosions. For stars, mass is destiny, and what will determine their ultimate fate is how much matter they can lose -- through stellar winds or as-yet-inexplicable eruptions -- before they run out of fuel and collapse under their own weight.

For now, the researchers say, there is no evidence to suggest an imminent demise of either star. They are exploring the rich dataset from the 2014 periastron passage to make new predictions, which will be tested when the stars again race together in February 2020.

NASA is exploring our solar system and beyond to understand the universe and our place in it. We seek to unravel the secrets of our universe, its origins and evolution, and search for life among the stars.

Related Link
 

·         Download this video and additional multimedia in HD formats from NASA Goddard's Scientific Visualization Studio

·         "Astronomers Bring the Third Dimension to a Doomed Star's Outburst" (07.08.2014)

·

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Maryland

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Goddard Space Flight Center, Hubble Space Telescope, RXTE (Rossi X-ray Timing Explorer), Stars, Swift, Universe,

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Solar System and Beyond

Nov. 20, 2014

NASA's Swift Satellite Marks 10 Years of Game-changing Astrophysics

Over the past decade, NASA's Swift Gamma-ray Burst Explorer has proven itself to be one of the most versatile astrophysics missions ever flown. It remains the only satellite capable of precisely locating gamma-ray bursts -- the universe's most powerful explosions -- and monitoring them across a broad range of wavelengths using multiple instruments before they fade from view.  

"Swift" isn't just a name -- it's a core capability, a part of the spacecraft's DNA. Gamma-ray bursts (GRBs) typically last less than a minute and Swift detects one event about twice a week. once Swift observes a GRB, it automatically determines the blast's location, broadcasts the position to the astronomical community, and then turns toward the site to investigate with its own sensitive telescopes.

"This process can take as little as 40 seconds, which is so quick we sometimes catch the tail end of the GRB itself," said John Nousek, the director of mission operations and a professor of astrophysics at Penn State University in University Park, Pennsylvania. "Because Swift autonomously responds to sudden bursts of high-energy light, it also provides us with data on a wide range of short-lived events, such as X-ray flares from stars and other objects."

From colliding asteroids to a star shredded by a monster black hole, this video showcases highlights from NASA Swift's decade of discovery.

Credits: NASA's Goddard Space Flight Center

Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

To date, Swift has detected more than 900 GRBs. Its discoveries include a new ultra-long class, whose high-energy emissions endure for hours; the farthest GRB, whose light took more than 13 billion years to reach us; and the "naked-eye" GRB, which for about a minute was bright enough to see with the naked-eye despite the fact that its light had traveled 7.5 billion years. Early in the mission, Swift observations provided the "smoking gun" that validated long-standing theoretical models suggesting that GRBs with durations under two seconds come from mergers of two neutron stars, objects with the mass of the sun that have been crushed to the size of a city.

In addition to its studies of GRBs, Swift conducts a wide array of observations of other astrophysical phenomena. A flexible planning system enables astronomers to request Swift "target-of-opportunity" (TOO) observations, which can be commanded from the ground in as little as 10 minutes, or set up monitoring programs to observe specific sources at time intervals ranging from minutes to months. The system can schedule up to 75 independent targets a day.

"These characteristics make Swift a pioneer in a burgeoning field we call 'time-domain' astronomy," said Neil Gehrels, the mission's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Just as we extended telescopic astronomy from visible light to other wavelengths, we are now beginning to study how the properties of astronomical objects change across a wide range of timescales, from less than a second to decades."  

In the most common type of gamma-ray burst, illustrated here, a dying massive star forms a black hole (left), which drives a particle jet into space. Light across the spectrum arises from hot gas near the black hole, collisions within the jet, and through the jet's interaction with its surroundings.

Credits: NASA's Goddard Space Flight Center

Some projects require years of observations, such as long-term monitoring of the center of our galaxy -- and its dormant supermassive black hole -- with Swift's X-Ray Telescope (XRT). Astronomers also are using the spacecraft's Burst Alert Telescope to conduct a continuing survey of more than 700 active galaxies, where monster black holes devour large amounts of gas and shine brightly in X-rays and gamma rays.

Shorter-term projects included observations to map the nearest galaxies in the ultraviolet. The most demanding object was the Large Magellanic Cloud, a small satellite galaxy orbiting our own at a distance of about 163,000 light-years. Swift's Ultraviolet/Optical Telescope (UVOT) captured 2,200 overlapping "snapshots" to cover the galaxy, producing the best-ever view in the UV. "The UVOT is the only telescope that can produce high-resolution wide-field multicolor surveys in the ultraviolet," said Michael Siegel, who leads the UVOT instrument team at Penn State.

Swift scientists discuss the mission, the science, and recall their personal experiences as members of the team.

Credits: NASA's Goddard Space Flight Center

Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

In 10 years of operation, Swift has made 315,000 individual observations of 26,000 separate targets, supporting nearly 6,200 TOO requests by more than 1,500 scientists. Its observations range from optical and ultraviolet studies of comets and asteroids to catching X-rays and gamma-rays from some of the most distant objects in the universe.

Another major highlight of Swift's studies of some 300 supernovae was the 2008 discovery of X-ray signals produced by a star caught in the act of exploding. Shockwaves breaching the surface of the dying star produced this brilliant flash.

Swift rocketed into orbit on Nov. 20, 2004. Managed by NASA Goddard, the mission is operated in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico, and Orbital Sciences Corporation in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy, with additional collaborators in Germany and Japan.

Earlier this year, Swift ranked highly in NASA's 2014 Senior Review of Operating Missions and will continue its enormously productive scientific work through at least 2016.

Related Links
 

·         Media gallery: Swift's Decade of Discovery

·         NASA Spacecraft Take Aim at Nearby Supernova (01.24.2014)

·         NASA Sees 'Watershed' Cosmic Blast in Unique Detail (11.21.2013)

·         NASA's Swift Produces Best Ultraviolet Maps of the Nearest Galaxies (06.03.2013)

·         NASA's Swift Reveals New Phenomenon in a Neutron Star (05.29.2013)

·         Researchers Detail How a Distant Black Hole Devoured a Star (08.24.2011)


Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Maryland

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Goddard Space Flight Center, Swift, Universe,

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Solar System and Beyond

Nov. 18, 2014

NASA's Swift Mission Probes an Exotic Object: ‘Kicked’ Black Hole or Mega Star?

 

Zoom into Markarian 177 and SDSS1133 and see how they compare with a simulated galaxy collision. When the central black holes in these galaxies combine, a "kick" launches the merged black hole on a wide orbit taking it far from the galaxy's core.

Credits:

Related multimedia from NASA Goddard's Scientific Visualization Studio

An international team of researchers analyzing decades of observations from many facilities, including NASA's Swift satellite, has discovered an unusual source of light in a galaxy some 90 million light-years away.

The dwarf galaxy Markarian 177 (center) and its unusual source SDSS1133 (blue) lie 90 million light-years away. The galaxies are located in the bowl of the Big Dipper, a well-known star pattern in the constellation Ursa Major.

Credits: Sloan Digital Sky Survey

Using the Keck II telescope in Hawaii, researchers obtained high-resolution images of Markarian 177 and SDSS1133 using a near-infrared filter. Twin bright spots in the galaxy's center are consistent with recent star formation, a disturbance that hints this galaxy may have merged with another.

Credits: Credit: W. M. Keck Observatory/M. Koss (ETH Zurich) et al.

Unlabeled version

SDSS1133 (bright spot, lower left) has been a persistent source for more than 60 years. This sequence of archival astronomical imagery, taken through different instruments and filters, shows that the source is detectable in 1950 and brightest in 2001.

Credits: NASA's Goddard Space Flight Center/M. Koss (ETH Zurich)

The object's curious properties make it a good match for a supermassive black hole ejected from its home galaxy after merging with another giant black hole. But astronomers can't yet rule out an alternative possibility. The source, called SDSS1133, may be the remnant of a massive star that erupted for a record period of time before destroying itself in a supernova explosion.

"With the data we have in hand, we can't yet distinguish between these two scenarios," said lead researcher Michael Koss, an astronomer at ETH Zurich, the Swiss Federal Institute of Technology. one exciting discovery made with NASA's Swift is that the brightness of SDSS1133 has changed little in optical or ultraviolet light for a decade, which is not something typically seen in a young supernova remnant." 

In a study published in the Nov. 21 edition of Monthly Notices of the Royal Astronomical Society, Koss and his colleagues report that the source has brightened significantly in visible light during the past six months, a trend that, if maintained, would bolster the black hole interpretation. To analyze the object in greater detail, the team is planning ultraviolet observations with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope in October 2015.

Whatever SDSS1133 is, it's persistent. The team was able to detect it in astronomical surveys dating back more than 60 years.

The mystery object is part of the dwarf galaxy Markarian 177, located in the bowl of the Big Dipper, a well-known star pattern within the constellation Ursa Major. Although supermassive black holes usually occupy galactic centers, SDSS1133 is located at least 2,600 light-years from its host galaxy's core.

In June 2013, the researchers obtained high-resolution near-infrared images of the object using the 10-meter Keck II telescope at the W. M. Keck Observatory in Hawaii. They reveal the emitting region of SDSS1133 is less than 40 light-years across and that the center of Markarian 177 shows evidence of intense star formation and other features indicating a recent disturbance.  

"We suspect we're seeing the aftermath of a merger of two small galaxies and their central black holes," said co-author Laura Blecha, an Einstein Fellow in the University of Maryland's Department of Astronomy and a leading theorist in simulating recoils, or "kicks," in merging black holes. "Astronomers searching for recoiling black holes have been unable to confirm a detection, so finding even one of these sources would be a major discovery."

The collision and merger of two galaxies disrupts their shapes and results in new episodes of star formation. If each galaxy possesses a central supermassive black hole, they will form a bound binary pair at the center of the merged galaxy before ultimately coalescing themselves.

Merging black holes release a large amount of energy in the form of gravitational radiation, a consequence of Einstein's theory of gravity. Waves in the fabric of space-time ripple outward in all directions from accelerating masses. If both black holes have equal masses and spins, their merger emits gravitational waves uniformly in all directions. More likely, the black hole masses and spins will be different, leading to lopsided gravitational wave emission that launches the black hole in the opposite direction.

The kick may be strong enough to hurl the black hole entirely out of its home galaxy, fating it to forever drift through intergalactic space. More typically, a kick will send the object into an elongated orbit. Despite its relocation, the ejected black hole will retain any hot gas trapped around it and continue to shine as it moves along its new path until all of the gas is consumed.

If SDSS1133 isn't a black hole, then it might have been a very unusual type of star known as a Luminous Blue Variable (LBV). These massive stars undergo episodic eruptions that cast large amounts of mass into space long before they explode. Interpreted in this way, SDSS1133 would represent the longest period of LBV eruptions ever observed, followed by a terminal supernova explosion whose light reached Earth in 2001. 

The nearest comparison in our galaxy is the massive binary system Eta Carinae, which includes an LBV containing about 90 times the sun's mass. Between 1838 and 1845, the system underwent an outburst that ejected at least 10 solar masses and made it the second-brightest star in the sky. It then followed up with a smaller eruption in the 1890s.

In this alternative scenario, SDSS1133 must have been in nearly continual eruption from at least 1950 to 2001, when it reached peak brightness and went supernova. The spatial resolution and sensitivity of telescopes prior to 1950 were insufficient to detect the source. But if this was an LBV eruption, the current record shows it to be the longest and most persistent one ever observed. An interaction between the ejected gas and the explosion's blast wave could explain the object's steady brightness in the ultraviolet.

Whether it's a rogue supermassive black hole or the closing act of a rare star, it seems astronomers have never seen the likes of SDSS1133 before.

Related Links:

Download HD video and print-resolution images from NASA Goddard's Scientific Visualization Studio
http://svs.gsfc.nasa.gov/goto?10082

Paper: "SDSS1133: an unusually persistent transient in a nearby dwarf galaxy"
http://mnras.oxfordjournals.org/content/445/1/515

Simulations Uncover 'Flashy' Secrets of Merging Black Holes (09.27.12)
http://www.nasa.gov/topics/universe/features/black-hole-secrets.html

Giant Black Hole Kicked Out of Home Galaxy (06.04.2012) 
http://www.nasa.gov/mission_pages/chandra/news/H-12-182.html

 

Francis Reddy

NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Karl Hille

Tags:  Black Holes, Goddard Space Flight Center, Swift, Universe,

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Swift

Sep. 29, 2014

NASA's Swift Mission Observes Mega Flares from a Mini Star

On April 23, NASA's Swift satellite detected the strongest, hottest, and longest-lasting sequence of stellar flares ever seen from a nearby red dwarf star. The initial blast from this record-setting series of explosions was as much as 10,000 times more powerful than the largest solar flare ever recorded.

"We used to think major flaring episodes from red dwarfs lasted no more than a day, but Swift detected at least seven powerful eruptions over a period of about two weeks," said Stephen Drake, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who gave a presentation on the "superflare" at the August meeting of the American Astronomical Society’s High Energy Astrophysics Division. "This was a very complex event."

At its peak, the flare reached temperatures of 360 million degrees Fahrenheit (200 million Celsius), more than 12 times hotter than the center of the sun.

In April 2014, NASA's Swift mission detected a massive superflare from a red dwarf star in the binary system DG CVn, located about 60 light-years away. Astronomers Rachel Osten of the Space Telescope Science Institute and Stephen Drake of NASA Goddard discuss this remarkable event.

Credits: NASA's Goddard Space Flight Center/S. Wiessinger

Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

The "superflare" came from one of the stars in a close binary system known as DG Canum Venaticorum, or DG CVn for short, located about 60 light-years away. Both stars are dim red dwarfs with masses and sizes about one-third of our sun's. They orbit each other at about three times Earth's average distance from the sun, which is too close for Swift to determine which star erupted.

"This system is poorly studied because it wasn't on our watch list of stars capable of producing large flares," said Rachel Osten, an astronomer at the Space Telescope Science Institute in Baltimore and a deputy project scientist for NASA's James Webb Space Telescope, now under construction. "We had no idea DG CVn had this in it."

Most of the stars lying within about 100 light-years of the solar system are, like the sun, middle-aged. But a thousand or so young red dwarfs born elsewhere drift through this region, and these stars give astronomers their best opportunity for detailed study of the high-energy activity that typically accompanies stellar youth. Astronomers estimate DG CVn was born about 30 million years ago, which makes it less than 0.7 percent the age of the solar system.

Stars erupt with flares for the same reason the sun does. Around active regions of the star's atmosphere, magnetic fields become twisted and distorted. Much like winding up a rubber band, these allow the fields to accumulate energy. Eventually a process called magnetic reconnection destabilizes the fields, resulting in the explosive release of the stored energy we see as a flare. The outburst emits radiation across the electromagnetic spectrum, from radio waves to visible, ultraviolet and X-ray light.

At 5:07 p.m. EDT on April 23, the rising tide of X-rays from DG CVn's superflare triggered Swift's Burst Alert Telescope (BAT). Within several seconds of detecting a strong burst of radiation, the BAT calculates an initial position, decides whether the activity merits investigation by other instruments and, if so, sends the position to the spacecraft. In this case, Swift turned to observe the source in greater detail, and, at the same time, notified astronomers around the globe that a powerful outburst was in progress.

"For about three minutes after the BAT trigger, the superflare's X-ray brightness was greater than the combined luminosity of both stars at all wavelengths under normal conditions," noted Goddard's Adam Kowalski, who is leading a detailed study on the event. "Flares this large from red dwarfs are exceedingly rare."

DG CVn, a binary consisting of two red dwarf stars shown here in an artist's rendering, unleashed a series of powerful flares seen by NASA's Swift. At its peak, the initial flare was brighter in X-rays than the combined light from both stars at all wavelengths under typical conditions.

Credits: NASA's Goddard Space Flight Center/S. Wiessinger

The star's brightness in visible and ultraviolet light, measured both by ground-based observatories and Swift's Optical/Ultraviolet Telescope, rose by 10 and 100 times, respectively. The initial flare's X-ray output, as measured by Swift's X-Ray Telescope, puts even the most intense solar activity recorded to shame.

The largest solar explosions are classified as extraordinary, or X class, solar flares based on their X-ray emission. "The biggest flare we've ever seen from the sun occurred in November 2003 and is rated as X 45," explained Drake. "The flare on DG CVn, if viewed from a planet the same distance as Earth is from the sun, would have been roughly 10,000 times greater than this, with a rating of about X 100,000."

But it wasn't over yet. Three hours after the initial outburst, with X-rays on the downswing, the system exploded with another flare nearly as intense as the first. These first two explosions may be an example of "sympathetic" flaring often seen on the sun, where an outburst in one active region triggers a blast in another.

Over the next 11 days, Swift detected a series of successively weaker blasts. Osten compares the dwindling series of flares to the cascade of aftershocks following a major earthquake. All told, the star took a total of 20 days to settle back to its normal level of X-ray emission.

How can a star just a third the size of the sun produce such a giant eruption? The key factor is its rapid spin, a crucial ingredient for amplifying magnetic fields. The flaring star in DG CVn rotates in under a day, about 30 or more times faster than our sun. The sun also rotated much faster in its youth and may well have produced superflares of its own, but, fortunately for us, it no longer appears capable of doing so.

Astronomers are now analyzing data from the DG CVn flares to better understand the event in particular and young stars in general. They suspect the system likely unleashes numerous smaller but more frequent flares and plan to keep tabs on its future eruptions with the help of NASA's Swift.

Related Links
 

·         Download the video in HD formats and print-resolution images from NASA Goddard's Scientific Visualization Studio

·         Swift Detection of a Superflare from DG CVn

·         X-Class: A Guide to Solar Flares

·         The Mouse That Roared: Pipsqueak Star Unleashes Monster Flare

·

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Maryland

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Goddard Space Flight Center, Stars, Swift, Universe,

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Solar System and Beyond

July 12, 2014

Out of An Hours-long Explosion, A Stand-In For The First Stars

In this artist's rendering of GRB 130925A, a sheath of hot, X-ray-emitting gas (red) surrounds a particle jet (white) blasting through the star's surface at nearly the speed of light. The source may have been a metal-poor blue supergiant, an important proxy for the universe's first stars.

Credits: NASA/Swift/A. Simonnet, Sonoma State Univ.

Astronomers analyzing a long-lasting blast of high-energy light observed in 2013 report finding features strikingly similar to those expected from an explosion from the universe's earliest stars. If this interpretation is correct, the outburst validates ideas about a recently identified class of gamma-ray burst and serves as a stand-in for what future observatories may see as the last acts of the first stars.

one of the great challenges of modern astrophysics has been the quest to identify the first generation of stars to form in the universe, which we refer to as Population III stars," explained lead scientist Luigi Piro, the director of research at the Institute for Space Astrophysics and Planetology in Rome, a division of Italy's National Institute for Astrophysics (INAF). "This important event takes us one step closer."

Gamma-ray bursts (GRBs) are the most luminous explosions in the universe. The blasts emit outbursts of gamma rays -- the most powerful form of light -- and X-rays, and produce rapidly fading afterglows that can be observed in visible light, infrared and radio wavelengths. on average, NASA's Swift satellite, Fermi Gamma-ray Space Telescope and other spacecraft detect about one GRB each day.

Shortly after 12:11 a.m. EDT on Sept. 25, 2013, Swift's Burst Alert Telescope triggered on a spike of gamma rays from a source in the constellation Fornax. The spacecraft automatically alerted observatories around the world that a new burst -- designated GRB 130925A, after the date -- was in progress and turned its X-ray Telescope (XRT) toward the source. Other satellites also detected the rising tide of high-energy radiation, including Fermi, the Russian Konus instrument onboard NASA's Wind spacecraft, and the European Space Agency's (ESA) INTEGRAL observatory.

The burst was eventually localized to a galaxy so far away that its light had been traveling for 3.9 billion years, longer than the oldest evidence for life on Earth.

A blue supergiant star, illustrated here, may be the most likely source of ultra-long gamma-ray bursts like GRB 130925A, which last hours rather than seconds. These stars contain about 20 times the sun's mass and may reach sizes large enough to span Jupiter's orbit.

Credits: NASA's Goddard Space Flight Center/S. Wiessinger

Unlabeled image

Astronomers have observed thousands of GRBs over the past five decades. Until recently, they were classified into two groups, short and long, based on the duration of the gamma-ray signal. Short bursts, lasting only two seconds or less, are thought to represent a merger of compact objects in a binary system, with the most likely suspects being neutron stars and black holes. Long GRBs may last anywhere from several seconds to several minutes, with typical durations between 20 and 50 seconds. These events are thought to be associated with the collapse of a star many times the sun's mass and the resulting birth of a new black hole.

GRB 130925A, by contrast, produced gamma rays for 1.9 hours, more than a hundred times greater than a typical long GRB. Observations by Swift's XRT revealed an intense and highly variable X-ray afterglow that exhibited strong flares for six hours, after which it finally began the steady fadeout usually seen in long GRBs.

"GRB 130925A is a member of a rare and newly recognized class we call ultra-long bursts," said Eleonora Troja, a visiting research scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a member of the study team. "But what really sets it apart is its unusual X-ray afterglow, which provides the strongest case yet that ultra-long GRBs come from stars called blue supergiants."

Astronomers think Wolf-Rayet stars best explain the origin of long GRBs. Born with more than 25 times the sun's mass, these stars burn so hot that they drive away their outer hydrogen envelopes through an outflow called a stellar wind. By the time it collapses, the star's outer atmosphere is essentially gone and its physical size is comparable to the sun's. A black hole forms in the star's core and matter falling toward it powers jets that burrow through the star. The jets continue operating for a few tens of seconds -- the time scale of long GRBs.

Because ultra-long GRBs last hundreds of times longer, the source star must have a correspondingly greater physical size. The most likely suspect, astronomers say, is a blue supergiant, a hot star with about 20 times the sun's mass that retains its deep hydrogen atmosphere, making it roughly 100 times the sun's diameter. Better yet, blue supergiants containing only a very small fraction of elements heavier than helium -- metals, in astronomical parlance -- could be substantially larger. A star's metal content controls the strength of its stellar wind, and this in turn determines how much of its hydrogen atmosphere it retains before collapse. For the largest blue supergiants, the hydrogen envelope would take hours to fall into the black hole, providing a sustained fuel source to power ultra-long GRBs.

Writing in the July 10 edition of The Astrophysical Journal Letters, the researchers note that radio observations of the GRB afterglow show that it displayed nearly constant brightness over a period of four months. This extremely slow decline suggests that the explosion's blast wave was moving essentially unimpeded through space, which means that the environment around the star is largely free of material cast off by a stellar wind.

The burst's long-lived X-ray flaring proved a more puzzling feature to explain, requiring observations from Swift, NASA's Chandra X-ray Observatory and ESA's XMM-Newton satellite to sort out. As the high-energy jet bores through the collapsing star, its leading edge rams into cooler stellar gas and heats it. This gas flows down the sides of the jet, surrounding it in a hot X-ray-emitting sheath. Because the jet travels a greater distance through a blue supergiant, this cocoon becomes much more massive than is possible in a Wolf-Rayet star. While the cocoon should expand rapidly as it exits the star, the X-ray evidence indicates that it remained intact. The science team suggests that magnetic fields may have suppressed the flow of hot gas across the cocoon, keeping it confined close to the jet.   

"This is the first time we have detected this thermal cocoon component, likely because all other known ultra-long bursts occurred at greater distances," said Piro.

The astronomers conclude that the best explanation for the unusual properties of GRB 130925A is that it heralded the death of a metal-poor blue supergiant, a model they suggest likely characterizes the entire ultra-long class.

Stars make heavy elements throughout their energy-producing lives and during their death throes in supernova explosions and GRBs. Each generation enriches interstellar gas with a greater proportion of metals, but the process is not uniform and metal-poor galaxies still exist nearby. Looking farther into the universe means looking deeper into the past, toward earlier stellar generations formed out of increasingly metal-poor gas. Astronomers think Population III stars ended their lives as blue supergiants, so GRB 130925A may prove to be a valuable nearby analog to phenomena we may one day detect from the universe's most distant stars.

Related Links

·         Paper: "A hot cocoon in the ultralong GRB 130925A: Hints of a Pop III-like progenitor in a low-density wind environment"

·         ESA press release: "Bizarre Nearby Blast Mimics Universe's Most Ancient Stars"

·         "Dying Supergiant Stars Implicated in Hours-long Gamma-Ray Bursts" (04.16.2013)

Francis Reddy
NASA's Goddard Space Flight Center

Last Updated: July 10, 2015

Editor: Lynn Jenner

Tags:  Chandra X-Ray Observatory, Goddard Space Flight Center, Swift, Universe,

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Black Holes

June 3, 2014

Black Hole ‘Batteries’ Keep Blazars Going and Going

Astronomers studying two classes of black-hole-powered galaxies monitored by NASA's Fermi Gamma-ray Space Telescope have found evidence that they represent different sides of the same cosmic coin. By unraveling how these objects, called blazars, are distributed throughout the universe, the scientists suggest that apparently distinctive properties defining each class more likely reflect a change in the way the galaxies extract energy from their central black holes.

"We can think of one blazar class as a gas-guzzling car and the other as an energy-efficient electric vehicle," said lead researcher Marco Ajello, an astrophysicist at Clemson University in South Carolina. "Our results suggest that we're actually seeing hybrids, which tap into the energy of their black holes in different ways as they age."

What astronomers once thought were two blazar families may in fact be one, as shown in this artist's concept. Energy stored in the black hole during its salad days of intense accretion may later be tapped by the blazar to continue its high-energy emissions long after this gas has been depleted.

Credits: NASA's Goddard Space Flight Center

Active galaxies possess extraordinarily luminous cores powered by black holes containing millions or even billions of times the mass of the sun. As gas falls toward these supermassive black holes, it settles into an accretion disk and heats up. Near the brink of the black hole, through processes not yet well understood, some of the gas blasts out of the disk in jets moving in opposite directions at nearly the speed of light.

Blazars are the highest-energy type of active galaxy and emit light across the spectrum, from radio to gamma rays. They make up more than half of the discrete gamma-ray sources cataloged by Fermi's Large Area Telescope, which has detected more than 1,000 to date. Astronomers think blazars appear so intense because they happen to tip our way, bringing one jet nearly into our line of sight. Looking almost directly down the barrel of a particle jet moving near the speed of light, emissions from the jet and the region producing it dominate our view.

To be considered a blazar, an active galaxy must show either rapid changes in visible light on timescales as short as a few days, strong optical polarization, or glow brightly at radio wavelengths with a "flat spectrum" — that is, one exhibiting relatively little change in brightness among neighboring frequencies.

Astronomers have identified two models in the blazar line. one, known as flat-spectrum radio quasars (FSRQs), show strong emission from an active accretion disk, much higher luminosities, smaller black hole masses and lower particle acceleration in the jets. The other, called BL Lacs, are totally dominated by the jet emission, with the jet particles reaching much higher energy and the accretion disk emission either weak or absent.

Speaking at the American Astronomical Society meeting in Boston on Tuesday, Ajello said he and his team wanted to probe how the distribution of these objects changed over the course of cosmic history, but solid distance information for large numbers of gamma-ray-producing BL Lac objects was hard to come by.

one of our most important tools for determining distance is the movement of spectral lines toward redder wavelengths as we look deeper into the cosmos," explained team member Dario Gasparrini, an astronomer at the Italian Space Agency's Science Data Center in Rome. "The weak disk emission from BL Lacs makes it extremely difficult to measure their redshift and therefore to establish a distance."

So the team undertook an extensive program of optical observations to measure the redshifts of BL Lac objects detected by Fermi.  

"This project has taken several years and simply wouldn't have been possible without the extensive use of many ground-based observatories by our colleagues," said team member Roger Romani, an astrophysicist at the Kavli Institute for Particle Astrophysics and Cosmology, a facility run jointly by Stanford University and the SLAC National Accelerator Laboratory in Menlo Park, California.

The redshift survey included 25 nights on the Hobby-Eberly Telescope at McDonald Observatory in Texas, led by Romani; eight nights on the 200-inch telescope at Palomar Observatory and nine nights on the 10-meter Keck Telescope in Hawaii, led by Anthony Readhead at Caltech in Pasadena, California; and nine nights on telescopes at the European Southern Observatory in Chile, led by Garret Cotter at the University of Oxford in England. In addition, important observations were provided by the Chile-based GROND camera, led by Jochen Greiner at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and the Ultraviolet/Optical Telescope on NASA's Swift satellite, led by Neil Gehrels at Goddard Space Flight Center in Greenbelt, Maryland.

With distances for about 200 BL Lacs in hand -- the largest and most comprehensive sample available to date -- the astronomers could compare their distribution across cosmic time with a similar sample of FSRQs. What emerged suggests that, starting around 5.6 billion years ago, FSRQs began to decline while BL Lacs underwent a steady increase in numbers. The rise is particularly noticeable among BL Lacs with the most extreme energies, which are known as high-synchrotron-peaked blazars based on a particular type of emission.

"What we think we're seeing here is a changeover from one style of extracting energy from the central black hole to another," adds Romani.

Large galaxies grew out of collisions and mergers with many smaller galaxies, and this process occurs with greater frequency as we look back in time. These collisions provided plentiful gas to the growing galaxy and kept the gas stirred up so it could more easily reach the central black hole, where it piled up into a vast, hot, and bright accretion disk like those seen in "gas-guzzling" FSRQs. Some of the gas near the hole powers a jet while the rest falls in and gradually increases the black hole's spin.

As the universe expands and the density of galaxies decreases, so do galaxy collisions and the fresh supply of gas they provide to the black hole. The accretion disk becomes depleted over time, but what's left is orbiting a faster-spinning and more massive black hole. These properties allow BL Lac objects to maintain a powerful jet even though relatively meager amounts of material are spiraling toward the black hole.

In effect, the energy of accretion from the galaxy's days as an FSRQ becomes stored in the increasing rotation and mass of its black hole, which acts much like a battery. When the gas-rich accretion disk all but disappears, the blazar taps into the black hole's stored energy that, despite a lower accretion rate, allows it to continue operating its particle jet and producing high-energy emissions as a BL Lac object.

One observational consequence of the hybrid blazar notion is that the luminosity of BL Lacs should decrease over time as the black hole loses energy and spins down.

The astronomers say they are eager to test this idea with larger blazar samples provided in part by Fermi's continuing all-sky survey. Understanding the details of this transition also will require better knowledge of the jet, the black hole mass and the galaxy environment for both blazar classes.

Related Links

·         Paper: “The Cosmic Evolution of Fermi BL Lacertae Objects”

·         Active Galaxies and Quasars at Imagine the Universe!

·         “NASA'S Fermi Measures Cosmic 'Fog' Produced by Ancient Starlight” (11.01.12)

·         “Fermi's Latest Gamma-ray Census Highlights Cosmic Mysteries” (09.09.11)

·         “Fermi Sees Brightest-Ever Blazar Flare” (12.08.09)

·

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Maryland

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Black Holes, Fermi Gamma-Ray Space Telescope, Goddard Space Flight Center, Universe,

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Black Holes

Feb. 20, 2014

RXTE Reveals the Cloudy Cores of Active Galaxies

Picture a single cloud large enough to span the solar system from the sun to beyond Pluto's orbit. Now imagine many such clouds orbiting in a vast ring at the heart of a distant galaxy, occasionally dimming the X-ray light produced by the galaxy's monster black hole.

Using data from NASA's Rossi X-ray Timing Explorer (RXTE) satellite, an international team has uncovered a dozen instances where X-ray signals from active galaxies dimmed as a result of a cloud of gas moving across our line of sight. The new study triples the number of cloud events previously identified in the 16-year archive.

Zoom into the cloudy heart of an active galaxy. This animation shows an artist's rendition of the cloudy structure revealed by a study of data from NASA's Rossi X-Ray Timing Explorer satellite.

Credits: NASA's Goddard Space Flight Center/Wolfgang Steffen, UNAM

Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

At the hearts of most big galaxies, including our own Milky Way, there lurks a supermassive black hole weighing millions to billions of times the sun's mass. As gas falls toward a black hole, it gathers into a so-called accretion disk and becomes compressed and heated, ultimately emitting X-rays. The centers of some galaxies produce unusually powerful emission that exceeds the sun's energy output by billions of times. These are active galactic nuclei, or AGN.

one of the great unanswered questions about AGN is how gas thousands of light-years away funnels into the hot accretion disk that feeds the supermassive black hole," said Alex Markowitz, an astrophysicist at the University of California, San Diego and the Karl Remeis Observatory in Bamberg, Germany. "Understanding the size, shape and number of clouds far from the black hole will give us a better idea of how this transport mechanism operates."

The study is the first statistical survey of the environments around supermassive black holes and is the longest-running AGN-monitoring study yet performed in X-rays. In the paper, which will appear in a future issue of Monthly Notices of the Royal Astronomical Society and is now published online, the scientists describe various properties of the occulting clouds, which vary in size and shape but average 4 billion miles (6.5 billion km) across – greater than Pluto's distance from the sun -- and twice the mass of Earth. They orbit a few light-weeks to a few light-years from the black hole.

RXTE's instruments measured variations in X-ray emission on timescales as short as microseconds and as long as years across a wide energy span, from 2,000 to 250,000 electron volts. For comparison, the energy of a typical dental X-ray is around 60,000 electron volts. NASA decommissioned the observatory in 2012, following 16 years of successful operation in Earth orbit.

"Because RXTE performed sustained observations of many of these AGN, our research is sensitive to a wide range of cloud events, from those as brief as five hours to as long as 16 years," said co-author Robert Nikutta, a theorist at Andrés Bello University in Santiago, Chile.

For decades, astronomers explained the different observed properties of AGN by suggesting that a relatively uniform "doughnut" of dust and gas surrounds the black hole and extends several light-years away from it. Interference from this material is lowest when we happen to be looking into the doughnut from above or below and greatest when we view it from the side. Now astronomers are moving toward a new generation of models that view the doughnut as a collection of many individual clouds mostly distributed along its central plane, a view supported by the RXTE study.

One of the more unusual events the team turned up occurred in NGC 3783, a barred spiral galaxy located 143 million light-years away toward the constellation Centaurus. "In 2008, the AGN dimmed twice over a period of 11 days and did not reach its typical X-ray brightness within that period," said co-author Mirko Krumpe of the European Southern Observatory in Garching, Germany. "This could be caused by an elongated, filamentary cloud, perhaps one that is in the process of being torn apart by the black hole."

Related Links

› Download HD video from NASA Goddard's Scientific Visualization Studio
› Paper: First X-ray-Based Statistical Tests for Clumpy-Torus Models: Eclipse Events from 230 Years of Monitoring of Seyfert AGN
› More about the Rossi X-Ray Timing Explorer
› "NASA's Rossi X-Ray Timing Explorer Completes Mission Operations" (01.09.12)
› Active Galaxies and Quasars: Imagine the Universe!
› "X-ray 'Echoes' Map a Supermassive Black Hole's Environs" (05.31.12)
› "Nearby Galaxy Boasts Two Monster Black Holes, Both Active" (06.10.11)
› Science in the Media Curriculum: Black Holes and Active Galaxies

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Black Holes, Goddard Space Flight Center, RXTE (Rossi X-ray Timing Explorer), Universe,

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Gamma-Ray Bursts

May 3, 2013

NASA's Fermi, Swift See 'Shockingly Bright' Burst

A record-setting blast of gamma rays from a dying star in a distant galaxy has wowed astronomers around the world. The eruption, which is classified as a gamma-ray burst, or GRB, and designated GRB 130427A, produced the highest-energy light ever detected from such an event.

"We have waited a long time for a gamma-ray burst this shockingly, eye-wateringly bright," said Julie McEnery, project scientist for the Fermi Gamma-ray Space Telescope at NASA's Goddard Space Flight Center in Greenbelt, Md. "The GRB lasted so long that a record number of telescopes on the ground were able to catch it while space-based observations were still ongoing."

The maps in this animation show how the sky looks at gamma-ray energies above 100 million electron volts (MeV) with a view centered on the north galactic pole. The first frame shows the sky during a three-hour interval prior to GRB 130427A. The second frame shows a three-hour interval starting 2.5 hours before the burst, and ending 30 minutes into the event. The Fermi team chose this interval to demonstrate how bright the burst was relative to the rest of the gamma-ray sky. This burst was bright enough that Fermi autonomously left its normal surveying mode to give the LAT instrument a better view, so the three-hour exposure following the burst does not cover the whole sky in the usual way.

Credits: NASA/DOE/Fermi LAT Collaboration

·         Side-by-side static image with labels

·         Unlabeled side-by-side image

Just after 3:47 a.m. EDT on Saturday, April 27, Fermi's Gamma-ray Burst Monitor (GBM) triggered on an eruption of high-energy light in the constellation Leo. The burst occurred as NASA's Swift satellite was slewing between targets, which delayed its Burst Alert Telescope's detection by less than a minute.

Fermi's Large Area Telescope (LAT) recorded one gamma ray with an energy of at least 94 billion electron volts (GeV), or some 35 billion times the energy of visible light, and about three times greater than the LAT's previous record. The GeV emission from the burst lasted for hours, and it remained detectable by the LAT for the better part of a day, setting a new record for the longest gamma-ray emission from a GRB.

This animation shows a more detailed Fermi LAT view of GRB 130427A. The sequence shows high-energy (100 Mev to 100 GeV) gamma rays from a 20-degree-wide region of the sky starting three minutes before the burst to 14 hours after. Following an initial one-second spike, the LAT emission remained relatively quiet for the next 15 seconds while Fermi's GBM instrument showed bright, variable lower-energy emission. Then the burst re-brightened in the LAT over the next few minutes and remained bright for nearly half a day.

Credits: NASA/DOE/Fermi LAT Collaboration

The burst subsequently was detected in optical, infrared and radio wavelengths by ground-based observatories, based on the rapid accurate position from Swift. Astronomers quickly learned that the GRB was located about 3.6 billion light-years away, which for these events is relatively close.

Swift's X-Ray Telescope took this 0.1-second exposure of GRB 130427A at 3:50 a.m. EDT on April 27, just moments after Swift and Fermi triggered on the outburst. The image is 6.5 arcminutes across.

Credits: NASA/Swift/Stefan Immler

Gamma-ray bursts are the universe's most luminous explosions. Astronomers think most occur when massive stars run out of nuclear fuel and collapse under their own weight. As the core collapses into a black hole, jets of material shoot outward at nearly the speed of light.

The jets bore all the way through the collapsing star and continue into space, where they interact with gas previously shed by the star and generate bright afterglows that fade with time.

If the GRB is near enough, astronomers usually discover a supernova at the site a week or so after the outburst.

"This GRB is in the closest 5 percent of bursts, so the big push now is to find an emerging supernova, which accompanies nearly all long GRBs at this distance," said Goddard's Neil Gehrels, principal investigator for Swift.

Ground-based observatories are monitoring the location of GRB 130427A and expect to find an underlying supernova by midmonth.

Related Links

·         Download additional graphics from NASA Goddard's Scientific Visualization Studio

·         Archive of GRB notices from the Gamma-ray Coordination Network

·         "NASA's Fermi Telescope Sees Most Extreme Gamma-ray Blast Yet" (02.19.09)

·         NASA's Fermi Gamma-ray Space Telescope

·         NASA's Swift mission

·

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Fermi Gamma-Ray Space Telescope, Gamma-Ray Bursts, Goddard Space Flight Center, Swift, Universe,

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Swift

Oct. 5, 2012

NASA's Swift Satellite Discovers a New Black Hole in our Galaxy

An X-ray outburst caught by NASA's Swift on Sept. 16, 2012, resulted from a flood of gas plunging toward a previously unknown black hole. Gas flowing from a sun-like star collects into a disk around the black hole. Normally, this gas would steadily spiral inward. But in this system, named Swift J1745-26, the gas collects for decades before suddenly surging inward.

Credits: NASA's Goddard Space Flight Center

Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

NASA's Swift satellite recently detected a rising tide of high-energy X-rays from a source toward the center of our Milky Way galaxy. The outburst, produced by a rare X-ray nova, announced the presence of a previously unknown stellar-mass black hole.

"Bright X-ray novae are so rare that they're essentially once-a-mission events and this is the first one Swift has seen," said Neil Gehrels, the mission's principal investigator, at NASA's Goddard Space Flight Center in Greenbelt, Md. "This is really something we've been waiting for."

An X-ray nova is a short-lived X-ray source that appears suddenly, reaches its emission peak in a few days and then fades out over a period of months. The outburst arises when a torrent of stored gas suddenly rushes toward one of the most compact objects known, either a neutron star or a black hole.

The rapidly brightening source triggered Swift's Burst Alert Telescope twice on the morning of Sept. 16, and once again the next day. 

Named Swift J1745-26 after the coordinates of its sky position, the nova is located a few degrees from the center of our galaxy toward the constellation Sagittarius. While astronomers do not know its precise distance, they think the object resides about 20,000 to 30,000 light-years away in the galaxy's inner region.

Ground-based observatories detected infrared and radio emissions, but thick clouds of obscuring dust have prevented astronomers from catching Swift J1745-26 in visible light.

The nova peaked in hard X-rays -- energies above 10,000 electron volts, or several thousand times that of visible light -- on Sept. 18, when it reached an intensity equivalent to that of the famous Crab Nebula, a supernova remnant that serves as a calibration target for high-energy observatories and is considered one of the brightest sources beyond the solar system at these energies.

Even as it dimmed at higher energies, the nova brightened in the lower-energy, or softer, emissions detected by Swift's X-ray Telescope, a behavior typical of X-ray novae. By Wednesday, Swift J1745-26 was 30 times brighter in soft X-rays than when it was discovered and it continued to brighten.

"The pattern we're seeing is observed in X-ray novae where the central object is a black hole. once the X-rays fade away, we hope to measure its mass and confirm its black hole status," said Boris Sbarufatti, an astrophysicist at Brera Observatory in Milan, Italy, who currently is working with other Swift team members at Penn State in University Park, Pa.

The black hole must be a member of a low-mass X-ray binary (LMXB) system, which includes a normal, sun-like star. A stream of gas flows from the normal star and enters into a storage disk around the black hole. In most LMXBs, the gas in the disk spirals inward, heats up as it heads toward the black hole, and produces a steady stream of X-rays. 

But under certain conditions, stable flow within the disk depends on the rate of matter flowing into it from the companion star. At certain rates, the disk fails to maintain a steady internal flow and instead flips between two dramatically different conditions -- a cooler, less ionized state where gas simply collects in the outer portion of the disk like water behind a dam, and a hotter, more ionized state that sends a tidal wave of gas surging toward the center.

"Each outburst clears out the inner disk, and with little or no matter falling toward the black hole, the system ceases to be a bright source of X-rays," said John Cannizzo, a Goddard astrophysicist. "Decades later, after enough gas has accumulated in the outer disk, it switches again to its hot state and sends a deluge of gas toward the black hole, resulting in a new X-ray outburst." 

This phenomenon, called the thermal-viscous limit cycle, helps astronomers explain transient outbursts across a wide range of systems, from protoplanetary disks around young stars, to dwarf novae -- where the central object is a white dwarf star -- and even bright emission from supermassive black holes in the hearts of distant galaxies. 

Swift, launched in November 2004, is managed by Goddard Space Flight Center. It is operated in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Va., with international collaborators in the United Kingdom and Italy and including contributions from Germany and Japan.

Related Link

·         Swift website

·

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Black Holes, Goddard Space Flight Center, Swift, Universe,

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Black Holes

Aug. 3, 2012

'Cry' of a Shredded Star Heralds a New Era for Testing Relativity

Last year, astronomers discovered a quiescent black hole in a distant galaxy that erupted after shredding and consuming a passing star. Now researchers have identified a distinctive X-ray signal observed in the days following the outburst that comes from matter on the verge of falling into the black hole.

This tell-tale signal, called a quasi-periodic oscillation or QPO, is a characteristic feature of the accretion disks that often surround the most compact objects in the universe -- white dwarf stars, neutron stars and black holes. QPOs have been seen in many stellar-mass black holes, and there is tantalizing evidence for them in a few black holes that may have middleweight masses between 100 and 100,000 times the sun's.

This illustration highlights the principal features of Swift J1644+57 and summarizes what astronomers have discovered about it.

Credits: NASA's Goddard Space Flight Center

Unlabeled image

Until the new finding, QPOs had been detected around only one supermassive black hole -- the type containing millions of solar masses and located at the centers of galaxies. That object is the Seyfert-type galaxy REJ 1034+396, which at a distance of 576 million light-years lies relatively nearby.

"This discovery extends our reach to the innermost edge of a black hole located billions of light-years away, which is really amazing. This gives us an opportunity to explore the nature of black holes and test Einstein's relativity at a time when the universe was very different than it is today," said Rubens Reis, an Einstein Postdoctoral Fellow at the University of Michigan in Ann Arbor. Reis led the team that uncovered the QPO signal using data from the orbiting Suzaku and XMM-Newton X-ray telescopes, a finding described in a paper published today in Science Express.

The X-ray source known as Swift J1644+57 -- after its astronomical coordinates in the constellation Draco -- was discovered on March 28, 2011, by NASA's Swift satellite. It was originally assumed to be a more common type of outburst called a gamma-ray burst, but its gradual fade-out matched nothing that had been seen before. Astronomers soon converged on the idea that what they were seeing was the aftermath of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and gobbled up a passing star. The galaxy is so far away that light from the event had to travel 3.9 billion years before reaching Earth.

On March 28, 2011, NASA's Swift detected intense X-ray flares thought to be caused by a black hole devouring a star. In one model, illustrated here, a sun-like star on an eccentric orbit plunges too close to its galaxy's central black hole. About half of the star's mass feeds an accretion disk around the black hole, which in turn powers a particle jet that beams radiation toward Earth.

Credits: NASA's Goddard Space Flight Center/Conceptual Image Lab

Download video in broadcast quality from NASA Goddard's Scientific Visualization Studio

The star experienced intense tides as it reached its closest point to the black hole and was quickly torn apart. Some of its gas fell toward the black hole and formed a disk around it. The innermost part of this disk was rapidly heated to temperatures of millions of degrees, hot enough to emit X-rays. At the same time, through processes still not fully understood, oppositely directed jets perpendicular to the disk formed near the black hole. These jets blasted matter outward at velocities greater than 90 percent the speed of light along the black hole's spin axis. one of these jets just happened to point straight at Earth.

Nine days after the outburst, Reis, Strohmayer and their colleagues observed Swift J1644+57 using Suzaku, an X-ray satellite operated by the Japan Aerospace Exploration Agency with NASA participation. About ten days later, they then began a longer monitoring campaign using the European Space Agency's XMM-Newton observatory.

"Because matter in the jet was moving so fast and was angled nearly into our line of sight, the effects of relativity boosted its X-ray signal enough that we could catch the QPO, which otherwise would be difficult to detect at so great a distance," said Tod Strohmayer, an astrophysicist and co-author of the study at NASA's Goddard Space Flight Center in Greenbelt, Md.

As hot gas in the innermost disk spirals toward a black hole, it reaches a point astronomers refer to as the innermost stable circular orbit (ISCO). Any closer to the black hole and gas rapidly plunges into the event horizon, the point of no return. The inward spiraling gas tends to pile up around the ISCO, where it becomes tremendously heated and radiates a flood of X-rays. The brightness of these X-rays varies in a pattern that repeats at a nearly regular interval, creating the QPO signal.

The data show that Swift J1644+57's QPO cycled every 3.5 minutes, which places its source region between 2.2 and 5.8 million miles (4 to 9.3 million km) from the center of the black hole, the exact distance depending on how fast the black hole is rotating. To put this in perspective, the maximum distance is only about 6 times the diameter of our sun. The distance from the QPO region to the event horizon also depends on rotation speed, but for a black hole spinning at the maximum rate theory allows, the horizon is just inside the ISCO.

"QPOs send us information from the very brim of the black hole, which is where the effects of relativity become most extreme," Reis said. "The ability to gain insight into these processes over such a vast distance is a truly beautiful result and holds great promise."

Related Links

·         "Researchers Detail How A Distant Black Hole Devoured A Star" (08.24.11)

·         Related visuals from NASA Goddard's Scientific Visualization Studio

·

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Black Holes, Goddard Space Flight Center, Stars, Swift, Universe,

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Black Holes

Aug. 24, 2011

Researchers Detail How a Distant Black Hole Devoured a Star

On March 28, 2011, NASA's Swift detected intense X-ray flares thought to be caused by a black hole devouring a star. In one model, illustrated here, a sun-like star on an eccentric orbit plunges too close to its galaxy's central black hole. About half of the star's mass feeds an accretion disk around the black hole, which in turn powers a particle jet that beams radiation toward Earth.

Credits: NASA/Goddard Space Flight Center/CI Lab

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Positions from Swift's XRT constrained the source to a small patch of sky that contains a faint galaxy known to be 3.9 billion light-years away. But to link the Swift event to the galaxy required observations at radio wavelengths, which showed that the galaxy's center contained a brightening radio source. Analysis of that source using the Expanded Very Large Array and Very Long Baseline Interferometry (VLBI) shows that it is still expanding at more than half the speed of light.

Credits: NRAO/CfA/Zauderer et al.

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WASHINGTON -- Two studies appearing in the Aug. 25 issue of the journal Nature provide new insights into a cosmic accident that has been streaming X-rays toward Earth since late March. NASA's Swift satellite first alerted astronomers to intense and unusual high-energy flares from the new source in the constellation Draco.

Swift's X-Ray Telescope continues to record high-energy flares from Swift J1644+57 more than three months after the source's first appearance. Astronomers believe that this behavior represents the slow depletion of gas in an accretion disk around a supermassive black hole. The first flares from the source likely coincided with the disk's creation, thought to have occurred when a star wandering too close to the black hole was torn apart.

Credits: NASA/Swift/Penn State

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"Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year," said David Burrows, professor of astronomy at Penn State University and lead scientist for the mission's X-Ray Telescope instrument. "It behaves unlike anything we've seen before."

Astronomers soon realized the source, known as Swift J1644+57, was the result of a truly extraordinary event -- the awakening of a distant galaxy's dormant black hole as it shredded and consumed a star. The galaxy is so far away, it took the light from the event approximately 3.9 billion years to reach Earth.

Burrows' study included NASA scientists. It highlights the X- and gamma-ray observations from Swift and other detectors, including the Japan-led Monitor of All-sky X-ray Image (MAXI) instrument aboard the International Space Station.

The second study was led by Ashley Zauderer, a post-doctoral fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. It examines the unprecedented outburst through observations from numerous ground-based radio observatories, including the National Radio Astronomy Observatory's Expanded Very Large Array (EVLA) near Socorro, N.M.

Most galaxies, including our own, possess a central supersized black hole weighing millions of times the sun's mass. According to the new studies, the black hole in the galaxy hosting Swift J1644+57 may be twice the mass of the four-million-solar-mass black hole in the center of the Milky Way galaxy. As a star falls toward a black hole, it is ripped apart by intense tides. The gas is corralled into a disk that swirls around the black hole and becomes rapidly heated to temperatures of millions of degrees.

The innermost gas in the disk spirals toward the black hole, where rapid motion and magnetism create dual, oppositely directed "funnels" through which some particles may escape. Jets driving matter at velocities greater than 90 percent the speed of light form along the black hole's spin axis. In the case of Swift J1644+57, one of these jets happened to point straight at Earth.

"The radio emission occurs when the outgoing jet slams into the interstellar environment," Zauderer explained. "By contrast, the X-rays arise much closer to the black hole, likely near the base of the jet."

Theoretical studies of tidally disrupted stars suggested they would appear as flares at optical and ultraviolet energies. The brightness and energy of a black hole's jet is greatly enhanced when viewed head-on. The phenomenon, called relativistic beaming, explains why Swift J1644+57 was seen at X-ray energies and appeared so strikingly luminous.

Wh

Images from Swift's Ultraviolet/Optical (white, purple) and X-Ray telescopes (yellow and red) were combined to make this view of Swift J1644+57. Evidence of the flares is seen only in the X-ray image, which is a 3.4-hour exposure taken on March 28, 2011.

Credits: NASA/Swift/Stefan Immler

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en first detected March 28, the flares were initially assumed to signal a gamma-ray burst, one of the nearly daily short blasts of high-energy radiation often associated with the death of a massive star and the birth of a black hole in the distant universe. But as the emission continued to brighten and flare, astronomers realized that the most plausible explanation was the tidal disruption of a sun-like star seen as beamed emission.

By March 30, EVLA observations by Zauderer's team showed a brightening radio source centered on a faint galaxy near Swift's position for the X-ray flares. These data provided the first conclusive evidence that the galaxy, the radio source and the Swift event were linked.

"Our observations show that the radio-emitting region is still expanding at more than half the speed of light," said Edo Berger, an associate professor of astrophysics at Harvard and a coauthor of the radio paper. "By tracking this expansion backward in time, we can confirm that the outflow formed at the same time as the Swift X-ray source."

Swift, launched in November 2004, is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. It is operated in collaboration with Penn State, the Los Alamos National Laboratory in N.M. and Orbital Sciences Corp., in Dulles, Va., with international collaborators in the U.K., Italy, Germany and Japan. MAXI is operated by the Japan Aerospace Exploration Agency as an external experiment attached to the Kibo module of the space station.

Related Links

·         Additional visuals

·         University of Leicester release

·         Max Planck Institute for Radio Astronomy release

·         Seoul National University release

·         INAF Release

This illustration steps through the events that scientists think likely resulted in Swift J1644+57.

Credits: NASA/Goddard Space Flight Center/Swift

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Text issued as NASA Release 11-271

Trent J. Perrotto
Headquarters, Washington
202-358-0321 
trent.j.perrotto@nasa.gov

Lynn Chandler
Goddard Space Flight Center, Greenbelt, Md.
301-286-2806
lynn.chandler-1@nasa.gov

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Black Holes, Stars, Swift, Universe,

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Swift

April 28, 2011

NASA's Swift and Hubble Probe Asteroid Collision Debris

In late 2010, images from the University of Arizona's Catalina Sky Survey, a project of NASA's Near Earth Object Observations Program, revealed an outburst from asteroid Scheila. Swift and Hubble then turned to it and caught the remnants of an asteroid smash-up just weeks after the collision occurred. (Star Wars: Episode V - The Empire Strikes Back™ & © 1980 and 1997 Lucasfilm Ltd. All rights reserved. Used under authorization. COURTESY OF LUCASFILM LTD.)

Credits: NASA's Goddard Space Flight Center

Download this video in HD formats from NASA Goddard's Scientific Visualization Studio

Late last year, astronomers noticed an asteroid named Scheila had unexpectedly brightened, and it was sporting short-lived plumes. Data from NASA's Swift satellite and Hubble Space Telescope showed these changes likely occurred after Scheila was struck by a much smaller asteroid.

Faint dust plumes bookend asteroid (596) Scheila, which is overexposed in this composite. Visible and ultraviolet images from Swift's UVOT (circled) are merged with a Digital Sky Survey image of the same region. The UVOT images were acquired on Dec. 15, 2010, when the asteroid was about 232 million miles from Earth.

Credits: NASA/Swift/DSS/D. Bodewits (UMD)

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The Hubble Space Telescope imaged (596) Scheila on Dec. 27, 2010, when the asteroid was about 218 million miles away. Scheila is overexposed in this image to reveal the faint dust features. The asteroid is surrounded by a C-shaped cloud of particles and displays a linear dust tail in this visible-light picture acquired by Hubble's Wide Field Camera 3. Because Hubble tracked the asteroid during the exposure, the star images are trailed.

Credits: NASA/ESA/D. Jewitt (UCLA)

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"Collisions between asteroids create rock fragments, from fine dust to huge boulders, that impact planets and their moons," said Dennis Bodewits, an astronomer at the University of Maryland in College Park and lead author of the Swift study. "Yet this is the first time we've been able to catch one just weeks after the smash-up, long before the evidence fades away."

Asteroids are rocky fragments thought to be debris from the formation and evolution of the solar system approximately 4.6 billion years ago. Millions of them orbit the sun between Mars and Jupiter in the main asteroid belt. Scheila is approximately 70 miles across and orbits the sun every five years.

"The Hubble data are most simply explained by the impact, at 11,000 mph, of a previously unknown asteroid about 100 feet in diameter," said Hubble team leader David Jewitt at the University of California in Los Angeles. Hubble did not see any discrete collision fragments, unlike its 2009 observations of P/2010 A2, the first identified asteroid collision.

The studies will appear in the May 20 edition of The Astrophysical Journal Letters and are available online.

Astronomers have known for decades that comets contain icy material that erupts when warmed by the sun. They regarded asteroids as inactive rocks whose destinies, surfaces, shapes and sizes were determined by mutual impacts. However, this simple picture has grown more complex over the past few years.

During certain parts of their orbits, some objects, once categorized as asteroids, clearly develop comet-like features that can last for many months. Others display much shorter outbursts. Icy materials may be occasionally exposed, either by internal geological processes or by an external one, such as an impact.

On Dec. 11, 2010, images from the University of Arizona's Catalina Sky Survey, a project of NASA's Near Earth Object Observations Program, revealed Scheila to be twice as bright as expected and immersed in a faint comet-like glow. Looking through the survey's archived images, astronomers inferred the outburst began between Nov. 11 and Dec. 3.

Three days after the outburst was announced, Swift's Ultraviolet/Optical Telescope (UVOT) captured multiple images and a spectrum of the asteroid. Ultraviolet sunlight breaks up the gas molecules surrounding comets; water, for example, is transformed into hydroxyl and hydrogen. But none of the emissions most commonly identified in comets, such as hydroxyl or cyanogen, show up in the UVOT spectrum. The absence of gas around Scheila led the Swift team to reject scenarios where exposed ice accounted for the activity.

Images show the asteroid was flanked in the north by a bright dust plume and in the south by a fainter one. The dual plumes formed as small dust particles excavated by the impact were pushed away from the asteroid by sunlight. Hubble observed the asteroid's fading dust cloud on Dec. 27, 2010, and Jan. 4, 2011.

The two teams found the observations were best explained by a collision with a small asteroid impacting Scheila's surface at an angle of less than 30 degrees, leaving a crater 1,000 feet across. Laboratory experiments show a more direct strike probably wouldn't have produced two distinct dust plumes. The researchers estimated the crash ejected more than 660,000 tons of dust - equivalent to nearly twice the mass of the Empire State Building.

"The dust cloud around Scheila could be 10,000 times as massive as the one ejected from comet 9P/Tempel 1 during NASA's UMD-led Deep Impact mission," said co-author Michael Kelley, also at the University of Maryland. "Collisions allow us to peek inside comets and asteroids. Ejecta kicked up by Deep Impact contained lots of ice, and the absence of ice in Scheila's interior shows that it's entirely unlike comets."

NASA's Goddard Space Flight Center in Greenbelt, Md., manages Hubble and Swift. Hubble was built and is operated in partnership with the European Space Agency. Science operations for both missions include contributions from many national and international partners.

For more information, video and images associated with this release, visit:

http://svs.gsfc.nasa.gov/goto?10747


Frank Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: NASA Administrator

Tags:  Asteroids, Goddard Space Flight Center, Hubble Space Telescope, Solar System, Swift, Universe,

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Suzaku

Dec. 11, 2009

Suzaku Catches Retreat of a Black Hole's Disk

GX 339-4, illustrated here, is among the most dynamic binaries in the sky, with four major outbursts in the past seven years. In the system, an evolved star no more massive than the sun orbits a black hole estimated at 10 solar masses.

Credits: ESO/L. Calçada

Studies of one of the galaxy's most active black-hole binaries reveal a dramatic change that will help scientists better understand how these systems expel fast-moving particle jets.

Binary systems where a normal star is paired with a black hole often produce large swings in X-ray emission and blast jets of gas at speeds exceeding one-third that of light. What fuels this activity is gas pulled from the normal star, which spirals toward the black hole and piles up in a dense accretion disk.

"When a lot of gas is flowing, the dense disk reaches nearly to the black hole," said John Tomsick at the University of California, Berkeley. "But when the flow is reduced, theory predicts that gas close to the black hole heats up, resulting in evaporation of the innermost part of the disk." Never before have astronomers shown an unambiguous signature of this transformation.

To look for this effect, Tomsick and an international group of astronomers targeted GX 339-4, a low-mass X-ray binary located about 26,000 light-years away in the constellation Ara. There, every 1.7 days, an evolved star no more massive than the sun orbits a black hole estimated at 10 solar masses. With four major outbursts in the past seven years, GX 339-4 is among the most dynamic binaries in the sky.

In September 2008, nineteen months after the system's most recent outburst, the team observed GX 339-4 using the orbiting Suzaku X-ray observatory, which is operated jointly by the Japan Aerospace Exploration Agency and NASA. At the same time, the team also observed the system with NASA's Rossi X-ray Timing Explorer satellite.

Instruments on both satellites indicated that the system was faint but in an active state, when black holes are known to produce steady jets. Radio data from the Australia Telescope Compact Array confirmed that GX 339-4's jets were indeed powered up when the satellites observed.

Despite the system's faintness, Suzaku was able to measure a critical X-ray spectral line produced by the fluorescence of iron atoms. "Suzaku's sensitivity to iron emission lines and its ability to measure the shapes of those lines let us see a change in the accretion disk that only happens at low luminosities," said team member Kazutaka Yamaoka at Japan's Aoyama Gakuin University.

X-ray photons emitted from disk regions closest to the black hole naturally experience stronger gravitational effects. The X-rays lose energy and produce a characteristic signal. At its brightest, GX 339-4's X-rays can be traced to within about 20 miles of the black hole. But the Suzaku observations indicate that, at low brightness, the inner edge of the accretion disk retreats as much as 600 miles.

"We see emission only from the densest gas, where lots of iron atoms are producing X-rays, but that emission stops close to the black hole - the dense disk is gone," explained Philip Kaaret at the University of Iowa. "What's really happening is that, at low accretion rates, the dense inner disk thins into a tenuous but even hotter gas, rather like water turning to steam."

The dense inner disk has a temperature of about 20 million degrees Fahrenheit, but the thin evaporated disk may be more than a thousand times hotter.

The study, which appears in the Dec. 10 issue of The Astrophysical Journal Letters, confirms the presence of low-density accretion flow in these systems. It also shows that GX 339-4 can produce jets even when the densest part of the disk is far from the black hole.

"This doesn't tell us how jets form, but it does tell us that jets can be launched even when the high-density accretion flow is far from the black hole," Tomsick said. "This means that the low-density accretion flow is the most essential ingredient for the formation of a steady jet in a black hole system."


Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Last Updated: July 10, 2015

Editor: Rob Garner

Tags:  Black Holes, Goddard Space Flight Center, Universe,

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