Giant black hole could upset galaxy evolution models

Nov. 27, 2012 — A group of astronomers led by Remco van den Bosch from the Max Planck Institute for Astronomy (MPIA) have discovered a black hole that could shake the foundations of current models of galaxy evolution. At 17 billion times the mass of the Sun, its mass is much greater than current models predict -- in particular since the surrounding galaxy is comparatively small. This could be the most massive black hole found to date.

To the best of our astronomical knowledge, almost every galaxy should contain in its central region what is called a supermassive black hole: a black hole with a mass between that of hundreds of thousands and billions of Suns. The best-studied super-massive black hole sits in the center of our home galaxy, the Milky Way, with a mass of about four million Suns.

For the masses of galaxies and their central black holes, an intriguing trend has emerged: a direct relationship between the mass of a galaxy's black hole and that of the galaxy's stars.

Typically, the black hole mass is a tiny fraction of the galaxy's total mass. But now a search led by Remco van den Bosch (MPIA) has discovered a massive black hole that could upset the accepted relationship between black hole mass and galaxy mass, which plays a key role in all current theories of galaxy evolution. The observations used the Hobby-Eberly Telescope and existing images from the Hubble Space Telescope.

With a mass 17 billion times that of the Sun, the newly discovered black hole in the center of the disk galaxy NGC 1277 might even be the biggest known black hole of all: the mass of the current record holder is estimated to lie between 6 and 37 billion solar masses (McConnell et al. 2011); if the true value lies towards the lower end of that range, NGC 1277 breaks the record. At the least, NGC 1277 harbors the second-biggest known black hole.

The big surprise is that the black hole mass for NGC 1277 amounts to 14% of the total galaxy mass, instead of usual values around 0,1%. This beats the old record by more than a factor 10. Astronomers would have expected a black hole of this size inside blob-like ("elliptical") galaxies ten times larger. Instead, this black hole sits inside a fairly small disk galaxy.

Is this surprisingly massive black hole a freak accident? Preliminary analysis of additional data suggests otherwise -- so far, the search has uncovered five additional galaxies that are comparatively small, yet, going by first estimates, seemed to harbor unusually large black holes too. More definite conclusions have to await detailed images of these galaxies.

If the additional candidates are confirmed, and there are indeed more black holes like this, astronomers will need to rethink fundamentally their models of galaxy evolution. In particular, they will need to look at the early universe: The galaxy hosting the new black hole appears to have formed more than 8 billion years ago, and does not appear to have changed much since then. Whatever created this giant black hole must have happened a long time ago.

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Journal Reference:

Remco C. E. van den Bosch, Karl Gebhardt, Kayhan Gültekin, Glenn van de Ven, Arjen van der Wel, Jonelle L. Walsh. An over-massive black hole in the compact lenticular galaxy NGC?1277. Nature, 2012; 491 (7426): 729 DOI: 10.1038/nature11592

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How black holes change gear

June 7, 2012 — Black holes are extremely powerful and efficient engines that not only swallow up matter, but also return a lot of energy to the Universe in exchange for the mass they eat. When black holes attract mass they also trigger the release of intense X-ray radiation and power strong jets. But not all black holes do this the same way. This has long baffled astronomers. By studying two active black holes researchers at the SRON Netherlands Institute for Space Research have now gathered evidence that suggests that each black hole can change between two different regimes, like changing the gears of an engine.

The team's findings will be published in two papers in the journal Monthly Notices of the Royal Astronomical Society.

Black hole jets -- lighthouse-like beams of material that race outwards at close to the speed of light -- can have a major impact on the evolution of their environment. For example, jets from the super-massive black holes found at the centre of galaxies can blow huge bubbles in and heat the gas found in clusters of galaxies.

Another stunning example of what black hole jets can do is known as Hanny's Voorwerp, a cloud of gas where stars started forming after it was hit by the jet-beam of a black hole in a neighbouring galaxy. These phenomena demonstrate the importance of research into the way black holes produce and distribute energy, but until recently, much of this has remained uncertain.

In 2003 it became clear from astronomical observations that there is a connection between the X-ray emission from a black hole and its jet outflow. This connection needs to be explained if we want to understand how the black hole engine works. In the first years after this connection was discovered, it seemed that it was the same for all feeding black holes, but soon oddballs were found. These unusual examples still have a clear connection between the energy released in the X-ray emission and that put in the jet ejection. But the proportion differs from that in the "standard" black holes. As the number of oddballs grew, it started to appear that there were two groups of black hole engines working in a slightly different way, as if one were running on petrol and the other on diesel.

For years astronomers struggled to justify this difference based on the properties of the two groups of black holes, but to no avail. Recently a step forward was made: a team of astronomers led by Michael Coriat (now at University of Southampton) found a black hole that seemed to switch between the two flavours of X-ray/jet connection, depending on its brightness changed. This suggested that black holes do not necessarily come with two different engines, but that each black hole can run in two different regimes, like two gears of the same engine.

Now Peter Jonker and PhD-student Eva Ratti, two researchers from the SRON Netherlands Institute for Space Research -- have taken an important step forward in the attempts to solve this puzzle. Using X-ray observations from the Chandra X-ray Observatory and radio observations from the Expanded Very Large Array in New Mexico they watched two black hole systems until their feeding frenzies ended.

Eva Ratti comments: "We found that these two black holes could also 'change gear', demonstrating that this is not an exceptional property of one peculiar black hole. Our work suggests that changing gear might be common among black holes. We also found that the switch between gears happens at a similar X-ray luminosity for all the three black holes."

These discoveries provide a new and important input to theoretical models that aim to explain both the functioning of the black hole engine itself and its impact on the surrounding environment.

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Journal References:

P. G. Jonker, J. C. A. Miller-Jones, J. Homan, J. Tomsick, R. P. Fender, P. Kaaret, S. Markoff, E. Gallo. The black hole candidate MAXI J1659-152 in and towards quiescence in X-ray and radio. Monthly Notices of the Royal Astronomical Society, 2012; DOI: 10.1111/j.1365-2966.2012.21116.xE. M. Ratti, P. G. Jonker, J. C. A. Miller-Jones, M. A. P. Torres, J. Homan, S. Markoff, J. A. Tomsick, P. Kaaret, R. Wijnands, E. Gallo, F. Özel, D. T. H. Steeghs, R. P. Fender. The black hole candidate XTE J1752-223 towards and in quiescence: optical and simultaneous X-ray-radio observations. Monthly Notices of the Royal Astronomical Society, 2012; DOI: 10.1111/j.1365-2966.2012.21071.x

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How to build a middleweight black hole: New model for intermediate black hole formation parallels growth of giant planets

July 19, 2012 — A new model shows how an elusive type of black hole can be formed in the gas surrounding their supermassive counterparts.

In research published in the Monthly Notices of the Royal Astronomical Society, scientists from the American Museum of Natural History, the City University of New York, the Jet Propulsion Laboratory of the California Institute of Technology, and the Harvard-Smithsonian Center for Astrophysics propose that intermediate-mass black holes -- light-swallowing celestial objects with masses ranging from hundreds to many thousands of times the mass of the Sun -- can grow in the gas disks around supermassive black holes in the centers of galaxies. The physical mechanism parallels the model astrophysicists use to describe the growth of giant planets in the gas disks surrounding stars.

"We know about small black holes, which tend to be close to us and have masses a few to 10 times that of our Sun, and we know about supermassive black holes, which are found in the centers of galaxies and have a mass that's millions to billions of times the mass of the sun," said coauthor Saavik Ford, who is a research associate in the Museum's Department of Astrophysics as well as a professor at the Borough of Manhattan Community College, City University of New York (CUNY) and a faculty member at CUNY's Graduate Center. "But we have no evidence for the middle stage. Intermediate-mass black holes are much harder to find."

The birth of an intermediate black hole starts with the death of a star that forms a stellar or low-mass black hole. In order for this "seed" to grow, it must collide with and consume other dead and living stars. But even though there are many billions of stars in large galaxies, there's an even greater proportion of empty space, making collisions a very rare occurrence.

The researchers' new model suggests that previous searches for middleweight black holes might have been focused on the wrong birthing ground.

"The recent focus had been on star clusters, but objects there move very quickly and there's no gas, which makes the chances of a collision very slim," said Barry McKernan, a research associate in the Museum's Department of Astrophysics who is a professor at CUNY's Borough of Manhattan Community College and a faculty member at CUNY's Graduate Center.

The new mechanism turns attention instead to active galactic nuclei, the piping hot and ultra-bright cores of galaxies that feed supermassive black holes. The gas in this system is key, causing the stars to slow down and conform to a circularized orbit.

"You can think of the stars as cars traveling on a 10-lane highway," McKernan said. "If there were no gas, the cars would be going at very different speeds and mostly staying in their lanes, making the odds of collision low. When you add gas, it slows the cars to matching speeds but also moves them into other lanes, making the odds of collision and consumption much higher."

The resulting collisions allow a stellar black hole to swallow stars and grow. The black hole's size and gravitational pull increase as its mass expands, escalating its chance of further collisions. This phenomenon, called "runaway growth," can lead to the creation of an intermediate-mass black hole.

As they increase in size, the black holes start altering the gas disk that controls them. The researchers' model shows that black holes of a certain mass can create a gap in the gas disk, a signature that might give scientists the first glimpse of intermediate black holes.

The model describing this growth is a scaled-up version of the mechanism for the formation of gas giant planets like Jupiter and Saturn. Like intermediate black holes, these planets are thought to have grown in gas disks. The planets, though, developed in disks surrounding newly forming stars. Mordecai-Mark Mac Low, chair of the Department of Astrophysics at the Museum, has modeled that case.

"In some regions, we showed that rocky planets could be moved by the gas into common orbits, where they collide to form objects more than ten times the mass of the Earth, massive enough to attract gas and form gas giant planets," Mac Low said. "The creative work described here applies the same principles to the far more massive disks found at the centers of galaxies, to form black holes rather than giant planets."

Other authors on the paper include Museum research associate Wladimir Lyra from the Jet Propulsion Laboratory at the California Institute of Technology and Hagai Perets from the Harvard-Smithsonian Center for Astrophysics.

This work was supported in part by NASA and CUNY.

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Journal Reference:

B. McKernan, K. E. S. Ford, W. Lyra, H. B. Perets. Intermediate mass black holes in AGN discs - I. Production and growth. Monthly Notices of the Royal Astronomical Society, 2012; DOI: 10.1111/j.1365-2966.2012.21486.x

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Super-massive black hole inflates giant bubble

Oct. 29, 2012 — Like symbiotic species, a galaxy and its central black hole lead intimately connected lives. The details of this relationship still pose many puzzles for astronomers.

Some black holes actively accrete matter. Part of this material do not fall into the black hole but is ejected in a narrow stream of particles, traveling at nearly the speed of light. When the stream slows down, it creates a tenuous bubble that can engulf the entire galaxy. Invisible to optical telescopes, the bubble is very prominent at low radio frequencies. The new International LOFAR Telescope - designed and built by ASTRON in an international collaboration - is ideally suited to detect this low frequency emission.

Astronomers have produced one of the best images ever of such a bubble, using LOFAR to detect frequencies from 20 to 160 MHz. "The result is of great importance", says Francesco de Gasperin, lead author of the study that is being published in the journal Astronomy & Astrophysics. "It shows the enormous potential of LOFAR, and provides compelling evidence of the close ties between black hole, host galaxy, and their surroundings."

The image was made during the test-phase of LOFAR, and targeted the giant elliptical galaxy Messier 87, at the centre of a galaxy cluster in the constellation of Virgo. This galaxy is 2000 times more massive than our Milky Way and hosts in its centre one of the most massive black holes discovered so far, with a mass six billion times that of our Sun. Every few minutes this black hole swallows an amount of matter similar to that of the whole Earth, converting part of it into radiation and a larger part into powerful jets of ultra-fast particles, which are responsible for the observed radio emission.

“This is the first time such high-quality images are possible at these low frequencies", says professor Heino Falcke, chairman of the board of the ILT and co-author of the study. "This was a challenging observation - we did not expect to get such fantastic results so early in the commissioning phase of LOFAR."

To determine the age of the bubble, the authors added radio observations at different frequencies from the Very Large Array in New Mexico (USA), and the Effelsberg 100-meter radio telescope near Bonn (Germany). The team found that this bubble is surprisingly young, just about 40 million years, which is a mere instant on cosmic time scales. The low frequency observation does not reveal any relic emission outside the well-confined bubble boundaries, this means that the bubble is not just a relic of an activity that happened long ago but is constantly refilled with fresh particles ejected by the central black hole.

"What is particularly fascinating", says Andrea Merloni from the Max-Planck Institute of Extraterrestrial Physics in Garching, who supervised de Gasperin's doctoral work, "is that the results also provide clues on the violent matter-to-energy conversion that occurs very close to the black hole. In this case the black hole is particularly efficient in accelerating the jet, and much less effective in producing visible emission."

Francesco de Gasperin performed the study as part of his PhD work at the Max Planck Institute for Astrophysics and at the Excellence Cluster Universe. De Gasperin is now a postdoctoral researcher at the University of Hamburg.

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Journal Reference:

F. de Gasperin, E. Orrú, M. Murgia, A. Merloni, H. Falcke, R. Beck, R. Beswick, L. Bîrzan, A. Bonafede, M. Brüggen, G. Brunetti, K. Chyzy, J. Conway, J. H. Croston, T. Enßlin, C. Ferrari, G. Heald, S. Heidenreich, N. Jackson, G. Macario, J. McKean, G. Miley, R. Morganti, A. Offringa, R. Pizzo, D. Rafferty, H. Röttgering, A. Shulevski, M. Steinmetz, C. Tasse, S. van der Tol, W. van Driel, R. J. van Weeren, J. E. van Zwieten, A. Alexov, J. Anderson, A. Asgekar, M. Avruch, M. Bell, M. R. Bell, M. Bentum, G. Bernardi, P. Best, F. Breitling, J. W. Broderick, A. Butcher, B. Ciardi, R. J. Dettmar, J. Eisloeffel, W. Frieswijk, H. Gankema, M. Garrett, M. Gerbers, J. M. Griessmeier, A. W. Gunst, T. E. Hassall, J. Hessels, M. Hoeft, A. Horneffer, A. Karastergiou, J. Köhler, Y. Koopman, M. Kuniyoshi, G. Kuper, P. Maat, G. Mann, M. Mevius, D. D. Mulcahy, H. Munk, R. Nijboer, J. Noordam, H. Paas, M. Pandey, V. N. Pandey, A. Polatidis, W. Reich, A. P. Schoenmakers, J. Sluman, O. Smirnov, C. Sobey, B. Stappers, J. Swinbank, M. Tagger, Y. Tang, I. van Bemmel, W. van Cappellen, A. P. van Duin, M. van Haarlem, J. van Leeuwen, R. Vermeulen, C. Vocks, S. White, M. Wise, O. Wucknitz, P. Zarka. M 87 at metre wavelengths: the LOFAR picture. Astronomy & Astrophysics, 2012; 547: A56 DOI: 10.1051/0004-6361/201220209

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Bonanza of black holes, hot DOGs: NASA's WISE survey uncovers millions of black holes

Aug. 29, 2012 — NASA's Wide-field Infrared Survey Explorer (WISE) mission has led to a bonanza of newfound supermassive black holes and extreme galaxies called hot DOGs, or dust-obscured galaxies.

Images from the telescope have revealed millions of dusty black hole candidates across the universe and about 1,000 even dustier objects thought to be among the brightest galaxies ever found. These powerful galaxies, which burn brightly with infrared light, are nicknamed hot DOGs.

"WISE has exposed a menagerie of hidden objects," said Hashima Hasan, WISE program scientist at NASA Headquarters in Washington. "We've found an asteroid dancing ahead of Earth in its orbit, the coldest star-like orbs known and now, supermassive black holes and galaxies hiding behind cloaks of dust."

WISE scanned the whole sky twice in infrared light, completing its survey in early 2011. Like night-vision goggles probing the dark, the telescope captured millions of images of the sky. All the data from the mission have been released publicly, allowing astronomers to dig in and make new discoveries.

The latest findings are helping astronomers better understand how galaxies and the behemoth black holes at their centers grow and evolve together. For example, the giant black hole at the center of our Milky Way galaxy, called Sagittarius A*, has 4 million times the mass of our sun and has gone through periodic feeding frenzies where material falls towards the black hole, heats up and irradiates its surroundings. Bigger central black holes, up to a billion times the mass of our sun, may even shut down star formation in galaxies.

In one study, astronomers used WISE to identify about 2.5 million actively feeding supermassive black holes across the full sky, stretching back to distances more than 10 billion light-years away. About two-thirds of these objects never had been detected before because dust blocks their visible light. WISE easily sees these monsters because their powerful, accreting black holes warm the dust, causing it to glow in infrared light.

"We've got the black holes cornered," said Daniel Stern of NASA's Jet Propulsion Laboratory, Pasadena, Calif., lead author of the WISE black hole study and project scientist for another NASA black-hole mission, the Nuclear Spectroscopic Telescope Array (NuSTAR). "WISE is finding them across the full sky, while NuSTAR is giving us an entirely new look at their high-energy X-ray light and learning what makes them tick."

In two other WISE papers, researchers report finding what are among the brightest galaxies known, one of the main goals of the mission. So far, they have identified about 1,000 candidates.

These extreme objects can pour out more than 100 trillion times as much light as our sun. They are so dusty, however, that they appear only in the longest wavelengths of infrared light captured by WISE. NASA's Spitzer Space Telescope followed up on the discoveries in more detail and helped show that, in addition to hosting supermassive black holes feverishly snacking on gas and dust, these DOGs are busy churning out new stars.

"These dusty, cataclysmically forming galaxies are so rare WISE had to scan the entire sky to find them," said Peter Eisenhardt, lead author of the paper on the first of these bright, dusty galaxies, and project scientist for WISE at JPL. "We are also seeing evidence that these record setters may have formed their black holes before the bulk of their stars. The 'eggs' may have come before the 'chickens.'"

More than 100 of these objects, located about 10 billion light-years away, have been confirmed using the W.M. Keck Observatory on Mauna Kea, Hawaii, as well as the Gemini Observatory in Chile, Palomar's 200-inch Hale telescope near San Diego, and the Multiple Mirror Telescope Observatory near Tucson, Ariz.

The WISE observations, combined with data at even longer infrared wavelengths from Caltech's Submillimeter Observatory atop Mauna Kea, revealed that these extreme galaxies are more than twice as hot as other infrared-bright galaxies. One theory is their dust is being heated by an extremely powerful burst of activity from the supermassive black hole.

"We may be seeing a new, rare phase in the evolution of galaxies," said Jingwen Wu of JPL, lead author of the study on the submillimeter observations. All three papers are being published in the Astrophysical Journal.

The three technical journal articles, including PDFs, can be found at http://arxiv.org/abs/1205.0811, http://arxiv.org/abs/1208.5517 and http://arxiv.org/abs/1208.5518 .

JPL manages and operates WISE for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing and archiving take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

More information is online at http://www.nasa.gov/wise, http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise .

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X-ray vision can reveal moment of birth of violent supernovae

Dec. 7, 2012 — A team of astronomers led by the University of Leicester has uncovered new evidence that suggests that X-ray detectors in space could be the first to witness new supernovae that signal the death of massive stars.

Astronomers have measured an excess of X-ray radiation in the first few minutes of collapsing massive stars, which may be the signature of the supernova shock wave first escaping from the star.

The findings have come as a surprise to Dr Rhaana Starling, of the University of Leicester Department of Physics and Astronomy whose research is published in the Monthly Notices of the Royal Astronomical Society.

Dr Starling said: "The most massive stars can be tens to a hundred times larger than the Sun. When one of these giants runs out of hydrogen gas it collapses catastrophically and explodes as a supernova, blowing off its outer layers which enrich the Universe. But this is no ordinary supernova; in the explosion narrowly confined streams of material are forced out of the poles of the star at almost the speed of light. These so-called relativistic jets give rise to brief flashes of energetic gamma-radiation called gamma-ray bursts, which are picked up by monitoring instruments in Space, that in turn alert astronomers."

Gamma-ray bursts are known to arise in stellar deaths because coincident supernovae are seen with ground-based optical telescopes about ten to twenty days after the high energy flash. The true moment of birth of a supernova, when the star's surface reacts to the core collapse, often termed the supernova shock breakout, is missed. Only the most energetic supernovae go hand-in-hand with gamma-ray bursts, but for this sub-class it may be possible to identify X-ray emission signatures of the supernova in its infancy. If the supernova could be detected earlier, by using the X-ray early warning system, astronomers could monitor the event as it happens and pinpoint the drivers behind one of the most violent events in our Universe.

The X-ray detectors being used for this research, built partly in the UK at the University of Leicester, are on the X-Ray Telescope on-board the Swift satellite. Swift is named after the bird because, like its namesake, it is able to swiftly turn around to catch a gamma-ray burst in action. Data from Swift of a number of gamma-ray bursts with visible supernovae have shown an excess in X-rays received compared with expectations. This excess is thermal emission, also known as blackbody radiation.

Dr Starling added: "We were surprised to find thermal X-rays coming from a gamma-ray burst, and even more surprising is that all confirmed cases so far are those with a secure supernova identification from optical data. This phenomenon is only seen during the first thousand seconds of an event, and it is challenging to distinguish it from X-ray emission solely from the gamma-ray burst jet. That is why astronomers have not routinely observed this before, and only a small subset of the 700+ bursts we detect with Swift show it."

"It all hangs on the positive identification of the extra X-ray radiation as directly emerging from the supernova shock front, rather than from the relativistic jets or central black hole. If this radiation turns out to be from the central black-hole-powered engine of the gamma-ray burst instead, it will still be a very illuminating result for gamma-ray burst physics, but the strong association with supernovae is tantalising."

The team, comprising scientists from the UK, Ireland, USA and Denmark, plan to extend their searches, and make more quantitative comparisons with theoretical models both for stellar collapse and the dynamics of fast jet-flows.

Astronomers will continue to view supernovae at their visible-light peak, when they are already tens of days old, but for the most energetic among them it may become possible to routinely witness the very moment they are born, through X-ray eyes.

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Journal References:

R. L. C. Starling, K. L. Page, A. Pe'er, A. P. Beardmore and J. P. Osborne. A search for thermal X-ray signatures in gamma-ray bursts – I. Swift bursts with optical supernovae. Monthly Notices of the Royal Astronomical Society, 28 NOV 2012 DOI: 10.1111/j.1365-2966.2012.22116.xMartin Sparre and Rhaana L. C. Starling. A search for thermal X-ray signatures in gamma-ray bursts – II. The Swift sample. Monthly Notices of the Royal Astronomical Society, 28 NOV 2012 DOI: 10.1111/j.1365-2966.2012.21858.x

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Black hole caught red-handed in a stellar homicide

May 2, 2012 — Astronomers have gathered the most direct evidence yet of a supermassive black hole shredding a star that wandered too close. NASA's Galaxy Evolution Explorer, a space-based observatory, and the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii were among the first to help identify the stellar remains.

Supermassive black holes, weighing millions to billions times more than the Sun, lurk in the centers of most galaxies. These hefty monsters lay quietly until an unsuspecting victim, such as a star, wanders close enough to get ripped apart by their powerful gravitational clutches.

Astronomers have spotted these stellar homicides before, but this is the first time they can identify the victim. Using a slew of ground- and space-based telescopes, a team of astronomers led by Suvi Gezari of The Johns Hopkins University in Baltimore, Md., has identified the victim as a star rich in helium gas. The star resides in a galaxy 2.7 billion light-years away.

Her team's results will appear in May 2 online edition of the journal Nature.

"When the star is ripped apart by the gravitational forces of the black hole, some part of the star's remains falls into the black hole, while the rest is ejected at high speeds. We are seeing the glow from the stellar gas falling into the black hole over time. We're also witnessing the spectral signature of the ejected gas, which we find to be mostly helium. It is like we are gathering evidence from a crime scene. Because there is very little hydrogen and mostly helium in the gas we detect, we know from the carnage that the slaughtered star had to have been the helium-rich core of a stripped star," Gezari explained.

This observation yields insights about the harsh environment around black holes and the types of stars swirling around them.

This is not the first time the unlucky star had a brush with the behemoth black hole. Gezari and her team think the star's hydrogen-filled envelope surrounding its core was lifted off a long time ago by the same black hole. In their scenario, the star may have been near the end of its life. After consuming most of its hydrogen fuel, it had probably ballooned in size, becoming a red giant. The astronomers think the bloated star was looping around the black hole in a highly elliptical orbit, similar to a comet's elongated orbit around the Sun. On one of its close approaches, the star was stripped of its puffed-up atmosphere by the black hole's powerful gravity. Only its core remained intact. The stellar remnant continued its journey around the black hole, until it ventured even closer to the behemoth monster and faced its ultimate demise.

Astronomers have predicted that stripped stars circle the central black hole of our Milky Way galaxy, Gezari pointed out. These close encounters, however, are rare, occurring roughly every 100,000 years. To find this one event, Gezari's team monitored hundreds of thousands of galaxies in ultraviolet light with NASA's Galaxy Evolution Explorer (GALEX), a space-based observatory, and in visible light with the Pan-STARRS1 telescope on the summit of Haleakala in Hawaii. Pan-STARRS, short for Panoramic Survey Telescope and Rapid Response System, scans the entire night sky for all kinds of transient phenomena, including supernovae.

The team was looking for a bright flare in ultraviolet light from the nucleus of a galaxy with a previously dormant black hole. They found one in June 2010, which was spotted with both telescopes. Both telescopes continued to monitor the flare as it reached peak brightness a month later and then slowly began to fade over the next 12 months. The brightening event was similar to that of a supernova, but the rise to the peak was much slower, taking nearly one and a half months.

"The longer the event lasted, the more excited we got, since we realized that this is either a very unusual supernova or an entirely different type of event, such as a star being ripped apart by a black hole," said team member Armin Rest of the Space Telescope Science Institute in Baltimore, Md.

By measuring the increase in brightness, the astronomers calculated the black hole's mass to be several million suns, which is comparable to the size of our Milky Way's black hole.

Spectroscopic observations with the MMT (Multiple Mirror Telescope) Observatory on Mount Hopkins in Arizona showed that the black hole was swallowing lots of helium. Spectroscopy divides light into its rainbow colors, which yields an object's characteristics, such as its temperature and gaseous makeup.

"The glowing helium was a tracer for an extraordinarily hot accretion event," Gezari said. "So that set off an alarm for us. And, the fact that no hydrogen was found set off a big alarm that this was not typical gas. You can't find gas like that lying around near the center of a galaxy. It's processed gas that has to have come from a stellar core. There's nothing about this event that could be easily explained by any other phenomenon."

The observed speed of the gas also linked the material to a black hole's gravitational pull. MMT measurements revealed that the gas was moving at more than 20 million miles an hour (over 32 million kilometers an hour). However, measurements of the speed of gas in the interstellar medium reveal velocities of only about 224,000 miles an hour (360,000 kilometers an hour).

"The place we also see these kinds of velocities are in supernova explosions," Rest said. "But the fact that it is still shining in ultraviolet light is incompatible with any supernova we know."

To completely rule out the possibility of an active nucleus flaring up in the galaxy, the team used NASA's Chandra X-ray Observatory to study the hot gas. Chandra showed that the characteristics of the gas didn't match those from an active galactic nucleus.

"This is the first time where we have so many pieces of evidence, and now we can put them all together to weigh the perpetrator (the black hole) and determine the identity of the unlucky star that fell victim to it," Gezari said. "These observations also give us clues to what evidence to look for in the future to find this type of event."

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Journal Reference:

S. Gezari, R. Chornock, A. Rest, M. E. Huber, K. Forster, E. Berger, P. J. Challis, J. D. Neill, D. C. Martin, T. Heckman, A. Lawrence, C. Norman, G. Narayan, R. J. Foley, G. H. Marion, D. Scolnic, L. Chomiuk, A. Soderberg, K. Smith, R. P. Kirshner, A. G. Riess, S. J. Smartt, C. W. Stubbs, J. L. Tonry, W. M. Wood-Vasey, W. S. Burgett, K. C. Chambers, T. Grav, J. N. Heasley, N. Kaiser, R.-P. Kudritzki, E. A. Magnier, J. S. Morgan, P. A. Price. An ultraviolet–optical flare from the tidal disruption of a helium-rich stellar core. Nature, 2012; DOI: 10.1038/nature10990

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X-ray 'echoes' map a supermassive black hole's environs in distant galaxies

May 31, 2012 — An international team of astronomers using data from the European Space Agency's (ESA) XMM-Newton satellite has identified a long-sought X-ray "echo" that promises a new way to probe supersized black holes in distant galaxies.

Most big galaxies host a big central black hole containing millions of times the sun's mass. When matter streams toward one of these supermassive black holes, the galaxy's center lights up, emitting billions of times more energy than the sun. For years, astronomers have been monitoring such "active galactic nuclei" (AGN) to better understand what happens on the brink of a monster black hole.

"Our analysis allows us to probe black holes through a different window. It confirms some long-held ideas about AGN and gives us a sense of what we can expect when a new generation of space-based X-ray telescopes eventually becomes available," said Abderahmen Zoghbi, a postdoctoral research associate at the University of Maryland at College Park (UMCP) and the study's lead author.

One of the most important tools for astronomers studying AGN is an X-ray feature known as the broad iron line, now regarded as the signature of a rotating black hole. Excited iron atoms produce characteristic X-rays with energies around 6,000 to 7,000 electron volts -- several thousand times the energy in visible light -- and this emission is known as the iron K line.

Matter falling toward a black hole collects into a rotating accretion disk, where it becomes compressed and heated before eventually spilling over the black hole's event horizon, the point beyond which nothing can escape and astronomers cannot observe. A mysterious and intense X-ray source near the black hole shines onto the disk's surface layers, causing iron atoms to radiate K-line emission. The inner part of the disk is orbiting the black hole so rapidly that the effects of Einstein's relativity come into play -- most notably, how time slows down close to the black hole. These relativistic effects skew or broaden the signal in a distinctive way.

Astronomers predicted that when the X-ray source near the black hole flared, the broad iron K line would brighten after a delay corresponding to how long the X-rays took to reach and illuminate the accretion disk. Astronomers call the process relativistic reverberation. With each flare from the X-ray source, a light echo sweeps across the disk and the iron line brightens accordingly.

Unfortunately, neither ESA's XMM-Newton satellite nor NASA's Chandra X-ray Observatory possess telescopes powerful enough to spot reverberations from individual flares.

he team reasoned that detecting the combined echoes from multiple flares might be possible if a sufficiently large amount of data from the right object could be analyzed. The object turned out to be the galaxy NGC 4151, which is located about 45 million light-years away in the constellation Canes Venatici. As one of the brightest AGN in X-rays, NGC 4151 has been observed extensively by XMM-Newton. Astronomers think that the galaxy's active nucleus is powered by a black hole weighing 50 million solar masses, which suggested the presence of a large accretion disk capable of producing especially long-lived and easily detectable echoes.

Since 2000, XMM-Newton has observed the galaxy with an accumulated exposure of about four days. By analyzing this data, the researchers uncovered numerous X-ray echoes, demonstrating for the first time the reality of relativistic reverberation. The findings appear in the May 8 issue of Monthly Notices of the Royal Astronomical Society.

The team found that echoes lagged behind the AGN flares by a little more than 30 minutes. Moving at the speed of light, the X-rays associated with the echo must have traveled an additional 400 million miles -- equivalent to about four times Earth's average distance from the sun -- than those that came to us directly from the flare.

"This tells us that the mysterious X-ray source in AGN hovers at some height above the accretion disk," said co-author Chris Reynolds, a professor of astronomy at UMCP and Zoghbi's adviser. Jets of accelerated particles often are associated with AGN, and this finding meshes with recent suggestions that the X-ray source may be located near the bases of these jets.

"The data show that the earliest echo comes from the most broadened iron line emission. This originates from closest to the black hole and fits well with expectations," said co-author Andy Fabian, an astrophysicist at the University of Cambridge in England.

Amazingly, the extreme environment at the heart of NGC 4151 is built on a scale comparable to our own solar system. If we replaced the sun with the black hole, the event horizon would extend less than halfway to Earth if the black hole spins rapidly; slower spin would result in a larger horizon. The X-ray source would hover above the black hole and its accretion disk at a distance similar to that between the sun and the middle of the asteroid belt.

"Teasing out the echo of X-ray light in NGC 4151 is a remarkable achievement. This work propels the science of AGN into a fundamental new area of mapping the neighborhoods of supermassive black holes," said Kimberly Weaver, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., who was not involved in the study. NASA Goddard hosts the XMM-Newton Guest Observer Facility, which supports U.S. astronomers who request observing time on the satellite.

The detection of X-ray echoes in AGN provides a new way of studying black holes and their accretion disks. Astronomers envision the next generation of X-ray telescopes with collecting areas large enough to detect the echo of a single AGN flare in many different objects, thereby providing astronomers with a new tool for testing relativity and probing the immediate surroundings of massive black holes.

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World's first glimpse of a black hole 'launchpad'

Sep. 27, 2012 — A strange thing about black holes: they shine.

The current issue of Science Express, the online advance publication of the journal, features a paper by the Event Horizon telescope team -- a collaboration which includes Perimeter Associate Faculty member Avery Broderick -- that may shed light on the origin of the bright jets given off by some black holes. In a world first, the team has been able to look at a distant black hole and resolve the area where its jets are launched from. This is the first empirical evidence to support the connection between black hole spin and black hole jets that has been long suspected on theoretical grounds.

Many galaxies, including our own Milky Way, have a huge black hole lurking at their cores. In about 10 percent of such galaxies, the hole gives off huge, tight streams of electrons and other sub-atomic particles traveling at nearly the speed of light. These powerful jets can extend for hundreds of thousands of light years. They can be so bright that they outshine the rest of the galaxy combined.

And yet, little is known about how such jets are formed. The Event Horizon team, in their current paper, is working to find out more. By combining and comparing data from three radio telescopes, they are beginning to image the base of such a jet -- its launchpad -- for the first time

The team, coordinated by Shep Doeleman at MIT's Haystack Observatory, used the Event Horizon telescope, which is actually a network of three radio telescopes spread out over Earth. The subject of their study is M87, a giant elliptical galaxy just over 50 million light years from our own. That is close as galaxies go, but a long way away considering that the horizon of the black hole the team imaged is about the same size as a single solar system. It is as if the telescope could make out a poppy seed from across a continent or spot a softball on the moon. "These are some of the highest resolutions ever accessed in the history of science," says Broderick.

Broderick sums up the problem the team tackled: "With black holes, stuff is supposed to go in, and yet here we see all this stuff coming out with huge energies. Where does that energy come from?"

There are two possibilities. The first is that a black hole itself is a great reservoir of energy -- a spinning black hole has a huge amount of rotational energy that the jets might tap. The second possibility is that the energy might come from some accretion process -- the accretion disk is the dusty spiral of stuff falling into the black hole and the physics of accretion is not yet well understood.

With the new data coming in from M87, theorists like Broderick can start to tell the difference between these models of hole-driven jets and accretion-driven jets. The image is not yet sharp -- it is trickling in pixel by pixel -- but that, says Broderick, "is enough to tell the difference between your mother and your daughter." With images like the one the team is working on, we can begin to narrow in on the origin of ultrarelativistic jets.

"The first thing we learned is that the launching region is quite small," says Broderick. The jets are coming from quite close to the black hole's event horizon: the point of no return where even the light from objects tumbling into the black hole is lost. While this is not quite enough to rule out the idea that jets might be powered by accretion physics, it is clear that energy is coming either from the black hole or from the accretion processes happening right next to the black hole.

"We are now beginning to see that spin is playing a role in jet production," says Broderick. "That is, not only can we say that the jets originate near the black hole, but because the emission region is so small, it must be coming from a rotating black hole."

"The black hole is really the engine that drives the jet," he adds. "It's an extraordinary thing."

Further exploration: http://www.eventhorizontelescope.org/

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The above story is reprinted from materials provided by Perimeter Institute for Theoretical Physics.

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Journal Reference:

Sheperd S. Doeleman, Vincent L. Fish, David E. Schenck, Christopher Beaudoin, Ray Blundell, Geoffrey C. Bower, Avery E. Broderick, Richard Chamberlin, Robert Freund, Per Friberg, Mark A. Gurwell, Paul T. P. Ho, Mareki Honma, Makoto Inoue, Thomas P. Krichbaum, James Lamb, Abraham Loeb, Colin Lonsdale, Daniel P. Marrone, James M. Moran, Tomoaki Oyama, Richard Plambeck, Rurik A. Primiani, Alan E. E. Rogers, Daniel L. Smythe, Jason SooHoo, Peter Strittmatter, Remo P. J. Tilanus, Michael Titus, Jonathan Weintroub, Melvyn Wright, Ken H. Young, and Lucy Ziurys. Jet-Launching Structure Resolved Near the Supermassive Black Hole in M87. Science, 2012; DOI: 10.1126/science.1224768

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Monster galaxy may have been stirred up by black-hole mischief

Oct. 25, 2012 — Astronomers using NASA's Hubble Space Telescope have obtained a remarkable new view of a whopper of an elliptical galaxy that may have been puffed up by the actions of one or more black holes in its core.

Spanning a little more than one million light-years, the galaxy is about 10 times the diameter of our Milky Way galaxy. The bloated galaxy is a member of an unusual class of galaxies with a diffuse core filled with a fog of starlight where there would normally be a concentrated peak of light around a central black hole. Viewing the core is like seeing a city with no downtown, just houses sprinkled across a vast landscape.

Astronomers used Hubble's Advanced Camera for Surveys and Wide Field Camera 3 to measure the amount of starlight across the galaxy, dubbed A2261-BCG. The Hubble observations revealed that the galaxy's puffy core, measuring about 10,000 light-years, is the largest yet seen.

A galaxy's core size typically is correlated to the dimensions of its host galaxy, but in this case, the central region is much larger than astronomers would expect for the galaxy's size. In fact, the bloated core is more than three times larger than the center of other very luminous galaxies. Located three billion light-years away, the galaxy is the most massive and brightest galaxy in the Abell 2261 cluster.

Astronomers have proposed two possibilities for the puffy core. One scenario is that a pair of merging black holes gravitationally stirred up and scattered the stars. Another idea is that the merging black holes were ejected from the core. Left without an anchor, the stars began spreading out even more, creating the puffy-looking core.

Previous Hubble observations have revealed that supermassive black holes, weighing millions or billions times more than the Sun, reside at the centers of nearly all galaxies and may play a role in shaping those central regions.

"Expecting to find a black hole in every galaxy is sort of like expecting to find a pit inside a peach," explained astronomer Tod Lauer of the National Optical Astronomy Observatory in Tucson, Ariz., a co-author of the Hubble study. "With this Hubble observation, we cut into the biggest peach and we can't find the pit. We don't know for sure that the black hole is not there, but Hubble shows that there's no concentration of stars in the core."

Team leader Marc Postman of the Space Telescope Science Institute in Baltimore, Md., said the galaxy stood out in the Hubble image. "When I first saw the image of this galaxy, I knew right away it was unusual," Postman explained. "The core was very diffuse and very large. The challenge was then to make sense of all the data, given what we knew from previous Hubble observations, and come up with a plausible explanation for the intriguing nature of this particular galaxy."

The paper describing the results appeared in the Sept. 10 issue of The Astrophysical Journal. The astronomers expected to see a slight cusp of light in the galaxy's center, marking the location of the black hole and attendant stars. Instead, the starlight's intensity remained fairly even across the galaxy.

One possibility for the puffy core may be due to two central black holes orbiting each other. These black holes collectively could have been as massive as several billion suns. Though one of the black holes would be native to the galaxy, a second black hole could have been added from a smaller galaxy that was gobbled up by the massive elliptical.

In this scenario, stars circling in the giant galaxy's center came close to the twin black holes. The stars were then given a gravitational boot out of the core. Each gravitational slingshot robbed the black holes of momentum, moving the pair ever closer together, until finally they merged, forming one supermassive black hole that still resides in the galaxy's center.

Another related possibility is that the black-hole merger created gravity waves, which are ripples in the fabric of space. According to the theory of general relativity, a pair of merging black holes produce ripples of gravity that radiate away. If the black holes are of unequal mass, then some of the energy may radiate more strongly in one direction, producing the equivalent of a rocket thrust. The imbalance of forces would have ejected the merged black hole from the center at speeds of millions of miles an hour, resulting in the rarity of a galaxy without a central black hole. "The black hole is the anchor for the stars," Lauer explained. "If you take it out, all of a sudden you have a lot less mass. The stars don't get held down very well and they expand out, enlarging the core even more."

The team admits that the ejected black-hole scenario may sound far-fetched, "but that's what makes observing the universe so intriguing -- sometimes you find the unexpected," said Postman.

Added Lauer: "This is a system that's interesting enough that it pushes against a lot of questions. We have thought an awful lot about what black holes do. But we haven't been able to test our theories. This is an interesting place where a lot of the ideas we've had can come together and can be tested, fairly exotic ideas about how black holes may interact with each other dynamically and how they would affect the surrounding stellar population."

The team is now conducting follow-up observations with the Very Large Array radio telescope (VLA) in New Mexico. The astronomers expect material falling onto a black hole to emit radio waves, among other types of radiation. They will compare the VLA data with the Hubble images to more precisely pin down the location of the black hole, if it indeed exists.

The Abell 2261 cluster is part of a multi-wavelength survey, led by Postman, called the Cluster Lensing And Supernova survey with Hubble (CLASH). The survey probes the distribution of dark matter in 25 massive galaxy clusters.

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, Md., manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Md., conducts Hubble science operations. STScI is operated by the Association of Universities for Research in Astronomy, Inc., in Washington.

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Measuring the universe’s 'exit door': For the first time, an international team has measured the radius of a black hole

Sep. 27, 2012 — The point of no return: In astronomy, it's known as a black hole -- a region in space where the pull of gravity is so strong that nothing, not even light, can escape. Black holes that can be billions of times more massive than our sun may reside at the heart of most galaxies. Such supermassive black holes are so powerful that activity at their boundaries can ripple throughout their host galaxies.

Now, an international team, led by researchers at MIT's Haystack Observatory, has for the first time measured the radius of a black hole at the center of a distant galaxy -- the closest distance at which matter can approach before being irretrievably pulled into the black hole.

The scientists linked together radio dishes in Hawaii, Arizona and California to create a telescope array called the "Event Horizon Telescope" (EHT) that can see details 2,000 times finer than what's visible to the Hubble Space Telescope. These radio dishes were trained on M87, a galaxy some 50 million light years from the Milky Way. M87 harbors a black hole 6 billion times more massive than our sun; using this array, the team observed the glow of matter near the edge of this black hole -- a region known as the "event horizon."

"Once objects fall through the event horizon, they're lost forever," says Shep Doeleman, assistant director at the MIT Haystack Observatory and research associate at the Smithsonian Astrophysical Observatory. "It's an exit door from our universe. You walk through that door, you're not coming back."

Doeleman and his colleagues have published the results of their study this week in the journal Science.

Jets at the edge of a black hole

Supermassive black holes are the most extreme objects predicted by Albert Einstein's theory of gravity -- where, according to Doeleman, "gravity completely goes haywire and crushes an enormous mass into an incredibly close space." At the edge of a black hole, the gravitational force is so strong that it pulls in everything from its surroundings. However, not everything can cross the event horizon to squeeze into a black hole. The result is a "cosmic traffic jam" in which gas and dust build up, creating a flat pancake of matter known as an accretion disk. This disk of matter orbits the black hole at nearly the speed of light, feeding the black hole a steady diet of superheated material. Over time, this disk can cause the black hole to spin in the same direction as the orbiting material.

Caught up in this spiraling flow are magnetic fields, which accelerate hot material along powerful beams above the accretion disk The resulting high-speed jet, launched by the black hole and the disk, shoots out across the galaxy, extending for hundreds of thousands of light-years. These jets can influence many galactic processes, including how fast stars form. 'Is Einstein right?'

A jet's trajectory may help scientists understand the dynamics of black holes in the region where their gravity is the dominant force. Doeleman says such an extreme environment is perfect for confirming Einstein's theory of general relativity -- today's definitive description of gravitation.

"Einstein's theories have been verified in low-gravitational field cases, like on Earth or in the solar system," Doeleman says. "But they have not been verified precisely in the only place in the universe where Einstein's theories might break down -- which is right at the edge of a black hole."

According to Einstein's theory, a black hole's mass and its spin determine how closely material can orbit before becoming unstable and falling in toward the event horizon. Because M87's jet is magnetically launched from this smallest orbit, astronomers can estimate the black hole's spin through careful measurement of the jet's size as it leaves the black hole. Until now, no telescope has had the magnifying power required for this kind of observation.

"We are now in a position to ask the question, 'Is Einstein right?'" Doeleman says. "We can identify features and signatures predicted by his theories, in this very strong gravitational field."

The team used a technique called Very Long Baseline Interferometry, or VLBI, which links data from radio dishes located thousands of miles apart. Signals from the various dishes, taken together, create a "virtual telescope" with the resolving power of a single telescope as big as the space between the disparate dishes. The technique enables scientists to view extremely precise details in faraway galaxies.

Using the technique, Doeleman and his team measured the innermost orbit of the accretion disk to be only 5.5 times the size of the black hole event horizon. According to the laws of physics, this size suggests that the accretion disk is spinning in the same direction as the black hole -- the first direct observation to confirm theories of how black holes power jets from the centers of galaxies.

The team plans to expand its telescope array, adding radio dishes in Chile, Europe, Mexico, Greenland and Antarctica, in order to obtain even more detailed pictures of black holes in the future.

Christopher Reynolds, a professor of astronomy at the University of Maryland, says the group's results provide the first observational data that will help scientists understand how a black hole's jets behave.

"The basic nature of jets is still mysterious," Reynolds says. "Many astrophysicists suspect that jets are powered by black hole spin ... but right now, these ideas are still entirely in the realm of theory. This measurement is the first step in putting these ideas on a firm observational basis."

This research was supported by the National Science Foundation.

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The above story is reprinted from materials provided by Massachusetts Institute of Technology. The original article was written by Jennifer Chu, MIT News Office.

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Journal Reference:

Sheperd S. Doeleman, Vincent L. Fish, David E. Schenck, Christopher Beaudoin, Ray Blundell, Geoffrey C. Bower, Avery E. Broderick, Richard Chamberlin, Robert Freund, Per Friberg, Mark A. Gurwell, Paul T. P. Ho, Mareki Honma, Makoto Inoue, Thomas P. Krichbaum, James Lamb, Abraham Loeb, Colin Lonsdale, Daniel P. Marrone, James M. Moran, Tomoaki Oyama, Richard Plambeck, Rurik A. Primiani, Alan E. E. Rogers, Daniel L. Smythe, Jason SooHoo, Peter Strittmatter, Remo P. J. Tilanus, Michael Titus, Jonathan Weintroub, Melvyn Wright, Ken H. Young, and Lucy Ziurys. Jet-Launching Structure Resolved Near the Supermassive Black Hole in M87. Science, 2012; DOI: 10.1126/science.1224768

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Measuring transient X-rays with lobster eyes

May 18, 2012 — A technology that mimics the structure of a lobster's eyes is now being applied to a new instrument that could help revolutionize X-ray astronomy and keep astronauts safe on the International Space Station.

Scientists at NASA's Goddard Space Flight Center in Greenbelt, Md., are developing the "Lobster Transient X-ray Detector," which they hope to deploy on the space station in three to four years. From its perch on the orbiting outpost, the cross-cutting instrument now being developed by Jordan Camp, Scott Barthelmy, and Gerry Skinner would detect with unprecedented accuracy transient X-rays -- those fleeting, hard-to-capture high-energy photons produced during black-hole and neutron-star mergers, supernovae, and gamma-ray bursts created much farther away in the early universe.

But the lobster-eye technology also could carry out another much-needed job.

It could check for ammonia leaks on the International Space Station -- a problem that engineers at NASA's Johnson Space Center in Houston, Texas, have identified as needing a solution. Anhydrous ammonia, a toxic compound of nitrogen and hydrogen, is used as a coolant that helps regulate the station's onboard temperatures. Currently, leaks are at acceptable levels, but a sudden increase could pose serious risks to astronauts, Camp said.

New Application for Established Technology

Lobster technology isn't new. First conceived as an X-ray all-sky monitor by University of Arizona scientist Roger Angel in the 1970s, it mimics the structure of the crustacean's eyes, which are made up of long, narrow cells that each captures a tiny amount of light, but from many different angles. Only then is the light focused into a single image.

The lobster X-ray instrument's optics would work the same way. Its eyes are a microchannel plate, a thin, curved slab of material dotted with tiny tubes across the surface. X-ray light enters these tubes from multiple angles and is focused through grazing-incident reflection, giving the technology a wide field of view necessary for finding and then imaging transient events that cannot be predicted in advance. The lobster detector is unique in that it is highly sensitive and provides a wide field of view and high-angular resolution, Camp said.

Since Angel first conceived the concept, astronomers at the University of Leicester in Leicester, England, have matured the technology and have built an instrument to fly on BepiColombo, a mission to Mercury developed jointly by the European Space Agency (ESA) and the Japan Aerospace Exploration Agency. ESA plans to launch the spacecraft in 2014.

What's new is "what we want to do with it," Camp said. "The innovation is using the lobster technology for a cross-cutting application. We want to use the technology in a new way to promote both astrophysics and human spaceflight."

To advance the dual-use concept, the team is using Goddard Internal Research and Development and NASA Office of the Chief Technologist's Center Innovation Fund support to assemble and test a prototype equipped with a commercially available microchannel plate, a charged-coupled device detector, and associated electronics.

Wide Field Collection of Transient X-rays

With its increased sensitivity and wide field of view, Camp said the instrument would be able to detect transient X-ray emissions from a large portion of the sky, giving scientists an unprecedented view of black-hole mergers, supernovae, and even gamma-ray bursts in the very distant universe. Transient X-rays are now difficult to detect because these sources brighten without warning and then vanish just as quickly.

He also believes the instrument could work in conjunction with and even extend the sensitivity of the Laser Interferometer Gravitational-Wave Observatory (LIGO), a National Science Foundation-funded experiment that has searched for gravitational waves since 2002. Gravitational waves, first postulated by Albert Einstein, are faint ripples in space-time that theoretically happen during massively powerful events, such as black-hole or neutron-star binary mergers.

Gravitational-wave detectors don't localize well. Used in conjunction with the focusing Lobster detector, however, scientists would be able to zero in on the location of the source, Camp said.

Detection of Ammonia Leaks on Space Station

Just as exciting, Camp said, is how he could use the technology to detect ammonia leaks. Anhydrous ammonia runs through tubing connected to huge radiator panels located outside the space station. As the ammonia circulates through the tubing, it releases heat as infrared radiation. In short, it helps to regulate onboard temperatures. Possibly because of micrometeorite impacts or thermal-mechanical stresses, these lines currently leak.

The lobster technology could help, Camp said. With this application, however, the instrument would require the addition of a specialized device called an electron gun, which would bombard surfaces with electron beams at specific energy levels. Elements that come into contact with these electron beams are excited, producing X-rays at specific energy levels.

In this case, the instrument, once attached to the space station's robotic arm, would sweep over the coolant lines and radiator panels in search of nitrogen, and more specifically the X-rays generated by the element. If nitrogen X-rays are detected, their presence could indicate leaks since ammonia is a compound of nitrogen and hydrogen.

Skinner has taken the lead in assembling and testing a leak-checking detector prototype and has recently succeeded in producing an X-ray image of a small nitrogen leak in a laboratory vacuum system. Barthelmy, meanwhile, is studying the system issues involved in deploying a dual-use lobster system on the space station.

"Many people are excited about the possibilities of this quintessentially cross-cutting instrument," Camp said. "With help from our IRAD program, we plan to advance the technology-readiness levels of our proposed instrument. We'll see where it goes. We believe it has great potential."

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Most quasars live on snacks, not large meals

June 19, 2012 — Black holes in the early universe needed a few snacks rather than one giant meal to fuel their quasars and help them grow, a new study shows.

Quasars are the brilliant beacons of light that are powered by black holes feasting on captured material, and in the process, heating some of the matter to millions of degrees. The brightest quasars reside in galaxies distorted by collisions with other galaxies. These encounters send lots of gas and dust into the gravitational whirlpool of hungry black holes.

Now, however, astronomers are uncovering an underlying population of fainter quasars that thrive in normal-looking spiral galaxies. They are triggered by black holes snacking on such tasty treats as a batch of gas or the occasional small satellite galaxy.

A census of 30 quasar host galaxies conducted with two of NASA's premier observatories, the Hubble Space Telescope and Spitzer Space Telescope, has found that 26 of the host galaxies bear no tell-tale signs of collisions with neighbors, such as distorted shapes. Only one galaxy in the sample shows evidence of an interaction with another galaxy. The galaxies existed roughly 8 billion to 12 billion years ago, during a peak epoch of black-hole growth.

The study, led by Kevin Schawinski of Yale University, bolsters evidence that the growth of most massive black holes in the early universe was fueled by small, long-term events rather than dramatic short-term major mergers.

"Quasars that are products of galaxy collisions are very bright," Schawinski said. "The objects we looked at in this study are the more typical quasars. They're a lot less luminous. The brilliant quasars born of galaxy mergers get all the attention because they are so bright and their host galaxies are so messed up. But the typical bread-and-butter quasars are actually where most of the black-hole growth is happening. They are the norm, and they don't need the drama of a collision to shine."

Schawinski's science paper has been accepted for publication in a letter to the Monthly Notices of the Royal Astronomical Society.

For his analysis, Schawinski analyzed galaxies observed by the Spitzer and Hubble telescopes in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). He chose 30 dust-enshrouded galaxies that appeared extremely bright in infrared images taken by the Spitzer telescope, a sign that their resident black holes are feasting on infalling material. The dust is blocking the quasar's light at visible wavelengths. But infrared light pierces the dust, allowing Schawinski to study the galaxies' detailed structure. The masses of those galaxies are comparable to our Milky Way's.

Schawinski then studied the galaxies in near-infrared images taken by Hubble's Wide Field Camera 3. Hubble's sharp images allowed careful analysis of galaxy shapes, which would be significantly distorted if major galaxy mergers had taken place and were disrupting the structure. Instead, in all but one instance, the galaxies show no such disruption.

Whatever process is stoking the quasars, it's below the detection capability of even Hubble. "I think it's a combination of processes, such as random stirring of gas, supernovae blasts, swallowing of small bodies, and streams of gas and stars feeding material into the nucleus," Schawinski said.

A black hole doesn't need much gas to satisfy its hunger and turn on a quasar. "There's more than enough gas within a few light-years from the center of our Milky Way to turn it into a quasar," Schawinski explained. "It just doesn't happen. But it could happen if one of those small clouds of gas ran into the black hole. Random motions and stirrings inside the galaxy would channel gas into the black hole. Ten billion years ago, those random motions were more common and there was more gas to go around. Small galaxies also were more abundant and were swallowed up by larger galaxies."

The galaxies in Schawinski's study are prime targets for the James Webb Space Telescope, a large infrared observatory scheduled to launch later this decade. "To get to the heart of what kinds of events are powering the quasars in these galaxies, we need the Webb telescope. Hubble and Spitzer have been the trailblazers for finding them."

The team of astronomers in this study consists of K. Schawinski, B.D. Simmons, C.M. Urry, and E. Glikman (Yale University), and E. Treister (Universidad de Concepción, Chile).

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Black holes as particle detectors

June 18, 2012 — Finding new particles usually requires high energies -- that is why huge accelerators have been built, which can accelerate particles to almost the speed of light. But there are other creative ways of finding new particles: At the Vienna University of Technology, scientists presented a method to prove the existence of hypothetical "axions." These axions could accumulate around a black hole and extract energy from it. This process could emit gravity waves, which could then be measured.

Axions are hypothetical particles with a very low mass. According to Einstein, mass is directly related to energy, and therefore very little energy is required to produce axions. "The existence of axions is not proven, but it is considered to be quite likely," says Daniel Grumiller. Together with Gabriela Mocanu he calculated at the Vienna University of Technology (Institute for Theoretical Physics), how axions could be detected.

Astronomically Large Particles

In quantum physics, every particle is described as a wave. The wavelength corresponds to the particle's energy. Heavy particles have small wavelengths, but the low-energy axions can have wavelengths of many kilometers. The results of Grumiller and Mocanu, based on works by Asmina Arvanitaki and Sergei Dubovsky (USA/Russia), show that axions can circle a black hole, similar to electrons circling the nucleus of an atom. Instead of the electromagnetic force, which ties the electrons and the nucleus together, it is the gravitational force which acts between the axions and the black hole.

The Boson-Cloud

However, there is a very important difference between electrons in an atom and axions around a black hole: Electrons are fermions -- which means that two of them can never be in the same state. Axions on the other hand are bosons, many of them can occupy the same quantum state at the same time. They can create a "boson-cloud" surrounding the black hole. This cloud continuously sucks energy from the black hole and the number of axions in the cloud increases.

Sudden Collapse

Such a cloud is not necessarily stable. "Just like a loose pile of sand, which can suddenly slide, triggered by one single additional grain of sand, this boson cloud can suddenly collapse," says Daniel Grumiller. The exciting thing about such a collapse is that this "bose-nova" could be measured. This event would make space and time vibrate and emit gravity waves. Detectors for gravity waves have already been developed, in 2016 they are expected to reach an accuracy at which gravity waves should be unambiguously detected. The new calculations in Vienna show that these gravity waves can not only provide us with new insights about astronomy, they can also tell us more about new kinds of particles.

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The above story is reprinted from materials provided by Vienna University of Technology. The original article was written by Gabriela Mocanu.

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Journal Reference:

Gabriela Mocanu, Daniel Grumiller. Self-organized criticality in boson clouds around black holes. Physical Review D, 2012; 85 (10) DOI: 10.1103/PhysRevD.85.105022

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Hubble spots a supernova in NGC 5806

Aug. 31, 2012 — A new image from the NASA/ESA Hubble Space Telescope shows NGC 5806, a spiral galaxy in the constellation Virgo (the Virgin). It lies around 80 million light years from Earth. Also visible in this image is a supernova explosion called SN 2004dg.

The exposures that are combined into this image were carried out in early 2005 in order to help pinpoint the location of the supernova, which exploded in 2004. The afterglow from this outburst of light, caused by a giant star exploding at the end of its life, can be seen as a faint yellowish dot near the bottom of the galaxy.

NGC 5806 was chosen to be one of a number of galaxies in a study into supernovae because Hubble's archive already contained high resolution imagery of the galaxy, collected before the star had exploded. Since supernovae are both relatively rare, and impossible to predict with any accuracy, the existence of such before-and-after images is precious for astronomers who study these violent events.

Aside from the supernova, NGC 5806 is a relatively unremarkable galaxy: it is neither particularly large or small, nor especially close or distant.

The galaxy's bulge (the densest part in the center of the spiral arms) is a so-called disk-type bulge, in which the spiral structure extends right to the center of the galaxy, instead of there being a large elliptical bulge of stars present. It is also home to an active galaxy nucleus, a supermassive black hole which is pulling in large amounts of matter from its immediate surroundings. As the matter spirals around the black hole, it heats up and emits powerful radiation.

This image is produced from three exposures in visible and infrared light, observed by Hubble's Advanced Camera for Surveys. The field of view is approximately 3.3 by 1.7 arcminutes.

A version of this image was entered into the Hubble's Hidden Treasures Image Processing Competition by contestant Andre van der Hoeven (who won second prize in the competition for his image of Messier 77). Hidden Treasures is an initiative to invite astronomy enthusiasts to search the Hubble archive for stunning images that have never been seen by the general public. The competition has now closed.

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Spacetime: A smoother brew than we knew

Aug. 23, 2012 — Spacetime may be less like beer and more like sipping whiskey. Or so an intergalactic photo finish would suggest.

Physicist Robert Nemiroff of Michigan Technological University reached this heady conclusion after studying the tracings of three photons of differing wavelengths that were recorded by NASA's Fermi Gamma-ray Space Telescope in May 2009.

The photons originated about 7 billion light years away from Earth in one of three pulses from a gamma-ray burst. They arrived at the orbiting telescope just one millisecond apart, in a virtual tie.

Gamma-ray bursts are short-lived bursts of gamma-ray photons, the most energetic form of light. They can originate far across the universe, and astronomers believe many are caused by giant stars collapsing, often billions of years before Earth was formed.

"Gamma-ray bursts can tell us some very interesting things about the universe," Nemiroff said. In this case, those three photons recorded by the Fermi telescope suggest that spacetime may not be not as bubbly as some scientists think.

Some theories of quantum gravity say that the universe is not smooth but foamy -- made of fundamental units called Planck lengths that are less than a trillionth of a trillionth the diameter of a hydrogen atom. Planck lengths are so small that there's no way to detect them, except via photons like those that make up gamma-ray bursts.

Here's why. The wavelengths of these photons are some of the shortest distances known to science -- so short they should interact with the even smaller Planck length. And if they interact, the photons should be dispersed -- scattered -- on their trek through Planck length-pixelated spacetime.

In particular, they should disperse in different ways if their wavelengths differ, just as a ping pong ball and a softball might take alternate paths down a gravely hillside.

You wouldn't notice the scattering over short distances, but across billions of light years, the Planck lengths should disperse the light. And three photons from the same gamma-ray burst should not have crashed through the Fermi telescope at the same moment.

But they did, and that calls into question just how foamy spacetime really is. "We have shown that the universe is smooth across the Planck mass," Nemiroff said. "That means that there's no choppiness that's detectable. It's a really cool discovery. We're very excited."

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The above story is reprinted from materials provided by Michigan Technological University. The original article was written by Marcia Goodrich.

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Journal Reference:

Robert Nemiroff, Ryan Connolly, Justin Holmes, Alexander Kostinski. Bounds on Spectral Dispersion from Fermi-Detected Gamma Ray Bursts. Physical Review Letters, 2012; 108 (23) DOI: 10.1103/PhysRevLett.108.231103

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Intense bursts of star formation drive fierce galactic winds

Aug. 20, 2012 — Fierce galactic winds powered by an intense burst of star formation may blow gas right out of massive galaxies, shutting down their ability to make new stars.

Sifting through images and data from three telescopes, a team of astronomers found 29 objects with outflowing winds measuring up to 2,500 kilometers per second, an order of magnitude faster than most observed galactic winds.

"They're nearly blowing themselves apart," said Aleksandar Diamond-Stanic, a fellow at the University of California's Southern California Center for Galaxy Evolution, who led the study. "Most galactic winds are more like fountains; the outflowing gas will fall back onto the galaxies. With the high-velocity winds we've observed the outflowing gas will escape the galaxy and never return."

Diamond-Stanic and colleagues published their findings in Astrophysical Journal Letters.

The galaxies they observed are a few billion light years away with outflowing winds of 500 to 2,500 kilometers per second. Initially they thought the winds might be coming from quasars, but a closer look revealed these winds emanate from entire galaxies.

Young, bright and compact, these massive galaxies are in the midst of or just completing a period of star formation as intense as anyone has ever observed.

"These galactic-scale crazy-fast winds are probably driven by the really massive stars exploding and pushing out the gas around them," said Alison Coil, professor in UC San Diego's Center for Astrophysics and Space Sciences and a co-author of the paper. "There's just such a high density of those stars it's like all these bombs went off near each other at the same time. Each bomb evacuates the area around it, then the next can push gas out further until they're evacuating gas on the scale of the whole galaxy."

Galaxies with winds this fast are also quite rare, opening up the question of whether these are unusual events or part of a common phase in the evolution of massive galaxies that is seldom observed because it is so brief.

Astrophysicists still lack an explanation for how and why star-making ends. Theorists who model the evolution of galaxies often invoke supermassive black holes called active galactic nuclei, which can also generate savage winds, to explain how gas needed to form stars can be depleted.

These new observations demonstrate that black holes may not be necessary to account for how these kinds galaxies run out of gas. "The winds seem to be powered by the starburst," Diamond-Stanic said. "The central supermassive black hole is apparently just a spectator for these massive stellar fireworks."

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Journal Reference:

Aleksandar M. Diamond-Stanic, John Moustakas, Christy A. Tremonti, Alison L. Coil, Ryan C. Hickox, Aday R. Robaina, Gregory H. Rudnick, Paul H. Sell. HIGH-VELOCITY OUTFLOWS WITHOUT AGN FEEDBACK: EDDINGTON-LIMITED STAR FORMATION IN COMPACT MASSIVE GALAXIES. The Astrophysical Journal, 2012; 755 (2): L26 DOI: 10.1088/2041-8205/755/2/L26

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NuSTAR space telescope opens its X-ray eyes

June 28, 2012 — NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has snapped its first test images of the sizzling high-energy X-ray universe. The observatory, launched June 13, is the first space telescope with the ability to focus high-energy X-rays, the same kind used by doctors and dentists, into crisp images.

Soon, the mission will begin its exploration of hidden black holes; fiery cinder balls left over from star explosions; and other sites of extreme physics in our cosmos.

"Today, we obtained the first-ever focused images of the high-energy X-ray universe," said Fiona Harrison, the mission's principal investigator at the California Institute of Technology in Pasadena, who first conceived of NuSTAR about 15 years ago. "It's like putting on a new pair of glasses and seeing aspects of the world around us clearly for the first time."

NuSTAR's lengthy mast, which provides the telescope mirrors and detectors with the distance needed to focus X-rays, was deployed on June 21. The NuSTAR team spent the next week verifying the pointing and motion capabilities of the satellite, and fine-tuning the alignment of the mast.

The first images from the observatory show Cygnus X-1, a black hole in our galaxy that is siphoning gas off a giant-star companion. This particular black hole was chosen as a first target because it is extremely bright in X-rays, allowing the NuSTAR team to easily see where the telescope's focused X-rays are falling on the detectors.

In the next two weeks, the team will point at two other bright calibration targets: G21.5-0.9, the remnant of a supernova explosion that occurred several thousand years ago in our own Milky Way galaxy; and 3C273, an actively feeding black hole, or quasar, located 2 billion light-years away at the center of another galaxy. These targets will be used to make a small adjustment to place the X-ray light at the optimum spot on the detector, and to further calibrate and understand the telescope in preparation for future science observations.

Other telescopes, including NASA's Swift and Chandra space telescopes, and the European Space Agency's XMM-Newton, will look at 3C273 in coordination with NuSTAR, helping to further calibrate the telescope.

The mission's primary observing program is expected to commence within two weeks.

"This is a really exciting time for the team," said Daniel Stern, the NuSTAR project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "We can already see the power of NuSTAR to crack open the high-energy X-ray universe and reveal secrets that were impossible to get at before."

Throughout its two-year prime mission, NuSTAR will turn its focused gaze on the most energetic objects in the universe, producing images with 100 times the sensitivity and 10 times the resolution of its predecessors operating at similar wavelength ranges. It will take a census of black holes both inside and outside of our Milky Way galaxy, and answer questions about how this enigmatic cosmic "species" behaves and evolves. Because it sees high-energy X-rays, NuSTAR will also probe farther into the dynamic regions around black holes, where matter is heated to temperatures as high as hundreds of millions of degrees, and will measure how fast black holes are spinning.

Other targets for the mission include the burnt-out remains of dead stars, such as those that exploded as supernovae; high-speed jets; the temperamental surface of our sun; and the structures where galaxies cluster together like mega-cities.

NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation, Dulles, Va. Its instrument was built by a consortium including Caltech; JPL; the University of California, Berkeley; Columbia University, New York; NASA's Goddard Space Flight Center, Greenbelt, Md.; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory, Livermore, Calif.; and ATK Aerospace Systems, Goleta, Calif. NuSTAR will be operated by UC Berkeley, with the Italian Space Agency providing its equatorial ground station located at Malindi, Kenya. The mission's outreach program is based at Sonoma State University, Rohnert Park, Calif. NASA's Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.

For more information, visit http://www.nasa.gov/nustar and http://www.nustar.caltech.edu/ .

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