Astronomers Find Most Distant Supermassive Black Hole Yet

Composite pseudo-color image of the QSO (CFHQSJ2329-0301). The RGB colors are assigned to z0; zr and i0-bands, respectively. The figures are north up, east left. Credit: Goto et al.

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A long time ago in a galaxy far, far away there was a supermassive black hole….. Astronomers from the University of Hawaii have spotted a giant galaxy surrounding the most distant supermassive black hole ever found. The galaxy, so distant that it is seen as it was 12.8 billion years ago, is as large as the Milky Way galaxy and harbors a supermassive black hole that contains at least a billion times as much matter as our Sun.

“It is surprising that such a giant galaxy existed when the Universe was only one-sixteenth of its present age,” said Dr. Tomotsugu Goto, “and that it hosted a black hole one billion times more massive than the Sun. The galaxy and black hole must have formed very rapidly in the early Universe.”

Knowledge of the host galaxies of supermassive black holes is important in order to understand the long-standing mystery of how galaxies and black holes have evolved together. Until now, studying host galaxies in the distant Universe has been extremely difficult because the blinding bright light from the vicinity of the black hole makes it more difficult to see the already faint light from the host galaxy.

The upper, middle, lower panels are for i0, z0 and zr-band, respectively.In each line, the left panels are reduced images. The middle panels are PSFs constructed using nearby stars. The right panels show residuals from the PSF subtraction. All figures are north up, east left.
The upper, middle, lower panels are for i0, z0 and zr-band, respectively.In each line, the left panels are reduced images. The middle panels are PSFs constructed using nearby stars. The right panels show residuals from the PSF subtraction. All figures are north up, east left.

To see the supermassive black hole, the team of scientists used new red-sensitive Charge Coupled Devices (CCDs) installed in the Suprime-Cam camera on the Subaru telescope on Mauna Kea. Prof. Satoshi Miyazaki of the National Astronomical Observatory of Japan (NAOJ) is a lead investigator for the creation of the new CCDs and a collaborator on this project. He said, “The improved sensitivity of the new CCDs has brought an exciting discovery as its very first result.”

The origin of the supermassive black holes remains an unsolved problem, and this new device and its findings could open a new window for investigating galaxy-black hole co-evolution at the dawn of the Universe.

A currently favored model requires several intermediate black holes to merge. The host galaxy discovered in this work provides a reservoir of such intermediate black holes. After forming, supermassive black holes often continue to grow because their gravity draws in matter from surrounding objects. The energy released in this process accounts for the bright light emitted from the region around the black holes.

A careful analysis of the data revealed that 40 percent of the near-infrared light observed (at the wavelength of 9100 Angstroms) is from the host galaxy itself and 60 percent is from the surrounding clouds of material (nebulae) illuminated by the black hole.

The scientists results will be published in the journal Monthly Notices of the Royal Astronomical Society later in September. Their paper is available here.

Source: RAS

If You Don’t Have an LHC, Here’s How to Create Your Own Black Hole

Artists concept of a black hole.

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Those fearful folks who have worried about the Large Hadron Collider creating a black hole that could swallow the Earth have probably been feeling pretty safe while the giant particle accelerator is still offline. But hopefully they haven’t read the latest Physical Review Letters . It includes a paper that explains how researchers at Dartmouth have figured out a way to create a tiny quantum-sized black hole in their lab, with no LHC required.

In their paper, the researchers show that a magnetic field-pulsed microwave transmission line containing an array of superconducting quantum interference devices, or SQUIDs, not only reproduces physics similar to that of a radiating black hole, but does so in a system where the high energy and quantum mechanical properties are well understood and can be directly controlled in the laboratory. The paper states, “Thus, in principle, this setup enables the exploration of analogue quantum gravitational effects.”

“We can also manipulate the strength of the applied magnetic field so that the SQUID array can be used to probe black hole radiation beyond what was considered by Hawking,” said Miles Blencowe, an author on the paper and a professor of physics and astronomy at Dartmouth.

Creating a black hole would allow researchers to better understand what physicist Stephen Hawking proposed more than 35 years ago: black holes are not totally void of activity; they emit photons, which is now known as Hawking radiation.

“Hawking famously showed that black holes radiate energy according to a thermal spectrum,” said co-author Paul Nation. “His calculations relied on assumptions about the physics of ultra-high energies and quantum gravity. Because we can’t yet take measurements from real black holes, we need a way to recreate this phenomenon in the lab in order to study it, to validate it.”

This is not the first proposed imitation black hole, Nation said. Other proposed schemes to create a black hole include using supersonic fluid flows, ultracold bose-einstein condensates and nonlinear fiber optic cables. However, these ideas wouldn’t work as well to study Hawking radiation because the radiation in these methods is incredibly weak or otherwise masked by commonplace radiation due to unavoidable heating of the device, making it very difficult to detect. “In addition to being able to study analogue quantum gravity effects, the new, SQUID-based proposal may be a more straightforward method to detect the Hawking radiation,” said Blencowe.

Source: Dartmouth U

Early Black Holes Are Starving, Not Feasting

Credit: KIPAC/SLAC/M. Alvarez, T. Abel and J. Wise

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A new black hole may not voraciously devour nearby gas — because it may kick out most of the gas in its neighborhood, a new study shows.

Marcelo Alvarez, of Stanford University, and his colleagues performed a new supercomputer simulation designed to track the fate of the universe’s first black holes. They found that, counter to expectations, young black holes couldn’t efficiently gorge themselves on nearby gas.

“The first stars were much more massive than most stars we see today, upwards of 100 times the mass of our sun,” said John Wise, a post-doctoral fellow at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and one of the study’s authors. “For the first time, we were able to simulate in detail what happens to the gas around those stars before and after they form black holes.”

The intense radiation and strong outflows from these massive stars caused nearby gas to dissipate. “These stars essentially cleared out most of the gas in their vicinity,” Wise said. A fraction of these first stars didn’t end their lives in grand supernovae explosions. Instead, they collapsed directly into black holes.

But the black holes were born into a gas-depleted cavity and, with little gas to feed on, they grew very slowly. “During the 200 million years of our simulation, a 100 solar-mass black hole grew by less than one percent of its mass,” Alvarez said.

Movie, credit KIPAC/SLAC/M. Alvarez, T. Abel and J. Wise
Movie, credit KIPAC/SLAC/M. Alvarez, T. Abel and J. Wise

Starting with data taken from observations of the cosmic background radiation — a flash of light that occurred 380,000 years after the big bang that presents the earliest view of cosmic structure — the researchers applied the basic laws that govern the interaction of matter and allowed their model of the early universe to evolve. The complex simulation included hydrodynamics, chemical reactions, the absorption and emission of radiation, and star formation.

In the simulation, cosmic gas slowly coalesced under the force of gravity and eventually formed the first stars. These massive, hot stars burned bright for a short time, emitting so much energy in the form of starlight that they pushed away nearby gas clouds.

These stars could not sustain such a fiery existence for long, and they soon exhausted their internal fuel. One of the stars in the simulation collapsed under its own weight to form a black hole. With only wisps of gas nearby, the black hole was essentially “starved” of matter on which to grow.

Yet, despite its strict diet, the black hole had a dramatic effect on its surroundings. This was revealed through a key aspect of the simulation called radiative feedback, which accounted for the way X-rays emitted by the black hole affected distant gas.

Even on a diet, a black hole produces copious X-rays. This radiation not only kept nearby gas from falling in, but it heated gas a hundred light-years away to several thousand degrees. Hot gas cannot come together to form new stars. “Even though the black holes aren’t growing significantly, their radiation is intense enough to shut off star formation nearby for tens and maybe even hundreds of millions of years,” said Alvarez.

Source: NASA. The study appears in The Astrophysical Journal Letters.

NASA Satellite Will Provide New Look At Cosmic X-Ray Sources

GEMS, the Gravity and Extreme Magnetism Small Explorer, will detect polarized X-rays from supernova remnants, neutron stars and black holes.

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NASA has announced the development of a space-based observatory to give astronomers a new way to view X-rays from exotic objects such as black holes, neutron stars, and supernovae.  Called the Gravity and Extreme Magnetism Small Explorer (GEMS), the mission is part of NASA’s Small Explorer (SMEX) series of cost-efficient and highly productive space-science satellites, and will be the first satellite to measure the polarization of X-rays sources beyond the solar system.

Polarization is the direction of the vibrating electric field in an electromagnetic wave. An everyday example of polarization is the attenuating effect of some types of sunglasses, which pass light that vibrates in one direction while blocking the rest.  Astronomers frequently measure the polarization of radio waves and visible light to get insight into the physics of stars, nebulae, and the interstellar medium, but few measurements have every been made of polarized X-rays from cosmic sources.

“To date, astronomers have measured X-ray polarization from only a single object outside the solar system — the famous Crab Nebula, the luminous cloud that marks the site of an exploded star,” said Jean Swank, a Goddard astrophysicist and the GEMS principal investigator. “We expect that GEMS will detect dozens of sources and really open up this new frontier.”

Black holes will be high on the list of objects for GEMS to observe.  The extreme gravitational field near a spinning black hole not only bends the paths of X-rays, it also alters the directions of their electric fields. Polarization measurements can reveal the presence of a black hole and provide astronomers with information on its spin. Fast-moving electrons emit polarized X-rays as they spiral through intense magnetic fields, providing GEMS with the means to explore another aspect of extreme environments.

“Thanks to these effects, GEMS can probe spatial scales far smaller than any telescope can possibly image,” Swank said. Polarized X-rays carry information about the structure of cosmic sources that isn’t available in any other way.

“GEMS will be about 100 times more sensitive to polarization than any previous X-ray observatory, so we’re anticipating many new discoveries,” said Sandra Cauffman, GEMS project manager and the Assistant Director for Flight Projects at Goddard.

Some of the fundamental questions scientists hope GEMS will answer include: Where is the energy released near black holes? Where do the X-ray emissions from pulsars and neutron stars originate? What is the structure of the magnetic fields in supernova remnants?

GEMS will have innovative detectors that efficiently measure X-ray polarization. Using three telescopes, GEMS will detect X-rays with energies between 2,000 and 10,000 electron volts. (For comparison, visible light has energies between 2 and 3 electron volts.) The telescope optics will be based on thin-foil X-ray mirrors developed at Goddard and already proven in the joint Japan/U.S. Suzaku orbital observatory.

GEMS will launch no earlier than 2014 on a mission lasting up to two years.  GEMS is expected to cost $105 million, excluding launch vehicle.

Orbital Sciences Corporation in Dulles, Va., will provide the spacecraft bus and mission operations. ATK Space in Goleta, Calif., will build a 4-meter deployable boom that will place the X-ray mirrors at the proper distance from the detectors once GEMS reaches orbit. NASA’s Ames Research Center in Moffett Field, Calif., will partner in the science, provide science data processing software and assist in tracking the spacecraft’s development.

Source: NASA Goddard

Also see Proposed Mission Could Study Space-Time Around Black Holes

Ejected Black Holes Drag Clusters of Stars With Them

This artist’s conception shows a rogue black hole that has been kicked out from the center of two merging galaxies. The black hole is surrounded by a cluster of stars that were ripped from the galaxies. Credit: Space Telescope Science Institute

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The tight cluster of stars surrounding a supermassive black hole after it has been violently kicked out of a galaxy represents a new kind of astronomical object which may provide telltale clues to how the ejection event occurred. “Hypercompact stellar systems” result when a supermassive black hole is violently ejected from a galaxy, following a merger with another supermassive black hole. The evicted black hole rips stars from the galaxy as it is thrown out. The stars closest to the black hole move in tandem with the massive object and become a permanent record of the velocity at which the kick occurred.

“You can measure how big the kick was by measuring how fast the stars are moving around the black hole,” said David Merritt, professor of physics at the Rochester Institute of Technolyg. “Only stars orbiting faster than the kick velocity remain attached to the black hole after the kick. These stars carry with them a kind of fossil record of the kick, even after the black hole has slowed down. In principle, you can reconstruct the properties of the kick, which is nice because there would be no other way to do it.”

In a paper published in the July 10 issue of The Astrophysical Journal, Merritt and his colleagues discusses the theoretical properties of these objects and suggests that hundreds of these faint star clusters might be detected at optical wavelengths in our immediate cosmic environment. Some of these objects may already have been picked up in astronomical surveys. .

“Finding these objects would be like discovering DNA from a long-extinct species,” said team member Stefanie Komossa, from the Max-Planck-Institut for Extraterrestrial Physics in Germany.

The astronomers say the best place to find hypercompact stellar systems is in cluster of galaxies like the nearby Coma and Virgo clusters. These dense regions of space contain thousands of galaxies that have been merging for a long time. Merging galaxies result in merging black holes, which is a prerequisite for the kicks.

“Even if the black hole gets kicked out of one galaxy, it’s still going to be gravitationally bound to the whole cluster of galaxies,” Merritt says. “The total gravity of all the galaxies is acting on that black hole. If it was ever produced, it’s still going to be there somewhere in that cluster.”

Merritt and his co-authors think that scientists may have already seen hypercompact stellar systems and not realized it. These objects would be easy to mistake for common star systems like globular clusters. The key signature making hypercompact stellar systems unique is a high internal velocity. This is detectable only by measuring the velocities of stars moving around the black hole, a difficult measurement that would require a long time exposure on a large telescope.

From time to time, a hypercompact stellar system will make its presence known in a much more dramatic way, when one of the stars is tidally disrupted by the supermassive black hole. In this case, gravity stretches the star and sucks it into the black hole. The star is torn apart, causing a beacon-like flare that signals a black hole. The possibility of detecting one of these “recoil flares” was first discussed in an August 2008 paper by co-authors Merritt and Komossa.

“The only contact of these floating black holes with the rest of the universe is through their armada of stars,” Merritt says, “with an occasional display of stellar fireworks to signal ‘here we are.’”

Source: Rochester Institute of Technology

Messier 87 Shows Off for Hundreds of Earth-bound Astronomers

Artists's Conception of M87's inner core: Black hole, accretion disk, and inner jets. Credit: Bill Saxton, NRAO/AUI/NSF

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When the giant radio galaxy Messier 87 (M 87) unleashed a torrent of gamma radiation and radio flux, an international collaboration of 390 scientists happened to be watching. They’re reporting the discovery in this week’s issue of Science Express.

Large-scale VLA image of M87: White circle indicates the area within which the gamma-ray telescopes could tell the very energetic gamma rays were being emitted. To narrow down the location further required the VLBA. CREDIT: NRAO/AUI/NSF
Large-scale VLA image of M87: White circle indicates the area within which the gamma-ray telescopes could tell the very energetic gamma rays were being emitted. To narrow down the location further required the VLBA. CREDIT: NRAO/AUI/NSF

The results give first experimental evidence that particles are accelerated to extremely high energies in the immediate vicinity of a supermassive black hole and then emit the observed gamma rays. The gamma rays have energies a trillion times higher than the energy of visible light.

Matthias Beilicke and Henric Krawczynski, both physicists at Washington University in St. Louis, coordinated the project using the Very Energetic Radiation Imaging Telescope Array System (VERITAS) collaboration. The effort involved three arrays of 12-meter (39-foot) to 17-meter (56-foot) telescopes, which detect very high-energy gamma rays, and the Very Long Baseline Array (VLBA) that detects radio waves with high spatial precision.

“We had scheduled gamma-ray observations of M 87 in a close cooperative effort with the three major gamma-ray observatories VERITAS, H.E.S.S. and MAGIC, and we were lucky that an extraordinary gamma-ray flare happened just when the source was observed with the VLBA and its impressive spatial resolving power,” Beilicke said.

“Only combining the high-resolution radio observations with the VHE gamma-ray observations allowed us to locate the site of the gamma-ray production,” added R. Craig Walker, a staff scientist at the National Radio Astronomy Observatory in Socorro, New Mexico.

Peering Deeper Into the Core of M87: At top left, a VLA image of the galaxy shows the radio-emitting jets at a scale of about 200,000 light-years. Subsequent zooms progress closer into the galaxy's core, where the supermassive black hole resides. In the artist's conception (background). the black hole illustrated at the center is about twice the size of our Solar System, a tiny fraction of the size of the galaxy, but holding some six billion times the mass of the Sun.  Credit: Bill Saxton, NRAO/AUI/NSF
Peering Deeper Into the Core of M87: At top left, a VLA image of the galaxy shows the radio-emitting jets at a scale of about 200,000 light-years. Subsequent zooms progress closer into the galaxy's core, where the supermassive black hole resides. In the artist's conception (background). the black hole illustrated at the center is about twice the size of our Solar System, a tiny fraction of the size of the galaxy, but holding some six billion times the mass of the Sun. Credit: Bill Saxton, NRAO/AUI/NSF

M 87 is located at a distance of 50 million light years from Earth in the Virgo cluster of galaxies. The black hole in the center of M 87 is six billion times more massive than the Sun.

The size of a non-rotating black hole is given by the Schwarzschild radius. Everything — matter or radiation — that comes within one Schwarzschild radius of the center of the black hole will be swallowed by it. The Schwarzschild radius of the supermassive black hole in M 87 is comparable to the radius of our Solar System.

In the case of some supermassive black holes — as in M 87 — matter orbiting and approaching the black hole powers highly relativistic outflows, called jets. The matter in the jets travels away from the black hole, escaping its deadly gravitational force. The jets are some of the largest objects in the Universe, and they can reach out many thousands of light years from the vicinity of the black hole into the intergalactic medium.

Very high-energy gamma-ray emission from M 87 was first discovered in 1998 with the HEGRA Cherenkov telescopes. “But even today, M 87 is one of only about 25 sources outside our galaxy known to emit [very high energy] gamma rays,” says Beilicke.

The new observations now show that the particle acceleration, and the subsequent emission of gamma rays, can happen in the very “inner jet,” less than about 100 Schwarzschild radii away from the black hole, which is an extremely narrow space as compared with the total extent of the jet or the galaxy.

In addition to VERITAS and the VLBA, the High Energy Stereoscopic System (H.E.S.S.) and the Major Atmospheric Gamma-Ray Imaging Cherenkov (MAGIC) gamma-ray observatories were involved in these observations.

Lead image caption: Artists’s Conception of M87’s inner core: Black hole, accretion disk, and inner jets. Credit: Bill Saxton, NRAO/AUI/NSF

Second image: Large-scale VLA image of M87: White circle indicates the area within which the gamma-ray telescopes could tell the very energetic gamma rays were being emitted. To narrow down the location further required the VLBA. CREDIT: NRAO/AUI/NSF

Collage: At top left, a VLA image of the galaxy shows the radio-emitting jets at a scale of about 200,000 light-years. Subsequent zooms progress closer into the galaxy’s core, where the supermassive black hole resides. In the artist’s conception (background). the black hole illustrated at the center is about twice the size of our Solar System, a tiny fraction of the size of the galaxy, but holding some six billion times the mass of the Sun. Credit: Bill Saxton, NRAO/AUI/NSF

Sources: Science and the National Radio Astronomy Observatory, via Eurekalert.

Astronomers Discover Medium-Sized Class of Black Holes

HLX-1 in the periphery of the edge-on spiral galaxy ESO 243-49. Credit: Heidi Sagerud.

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It’s the Goldilocks variety of black holes: not too big and not too small.

The new source HLX-1,  the light blue object to the top left of the galactic bulge, is the ambassador for a new class of black holes, more than 500 times the mass of the Sun. It lies on the periphery of the edge-on spiral galaxy ESO 243-49, about 290 million light years from Earth.

The discovery, led by Sean Farrell at Britain’s University of Leicester, appears today in the journal Nature.

Until now, identified black holes have been either super-massive (several million to several billion times the mass of the Sun) in the center of galaxies, or about the size of a typical star (between three and 20 solar masses).

The new discovery is the first solid evidence of a new class of medium-sized black holes and was made using the European Space Agency’s XMM-Newton X-ray space telescope. At the time of the discovery, Farrell and his team were working at the Centre d’Etude Spatiale des Rayonnements in France.

black hole is a remnant of a collapsed star with such a powerful gravitational field that it absorbs all the light that passes near it and reflects nothing.

“While it is widely accepted that stellar mass black holes are created during the death throes of massive stars, it is still unknown how super-massive black holes are formed,” Farrell said.

It had been long believed by astrophysicists that there might be a third, intermediate class of black holes, with masses between a hundred and several hundred thousand times that of the Sun. However, such black holes had not been reliably detected until now.

One theory suggests that super-massive black holes may be formed by the merger of a number of intermediate mass black holes, Farrell said.

“To ratify such a theory, however, you must first prove the existence of intermediate black holes. This is the best detection to date of such long sought after intermediate mass black holes. ”

Using XMM-Newton observations carried out in 2004 and 2008, the team showed that HLX-1 displayed a variation in its X-ray signature. This indicated that it must be a single object and not a group of many fainter sources. The huge radiance observed can only be explained if HLX-1 contains a black hole more than 500 times the mass of the Sun. The authors say that no other physical explanation can account for the data.

Lead image caption: Artist’s impression of HLX-1 in the periphery of the edge-on spiral galaxy ESO 243-49. Credit: Heidi Sagerud.

Sources: Nature and the University of Leicester

Mysterious “Blobs” Are Windows Into Galaxy Formation

Credit: Left panel: X-ray (NASA/CXC/Durham Univ./D.Alexander et al.); Optical (NASA/ESA/STScI/IoA/S.Chapman et al.); Lyman-alpha Optical (NAOJ/Subaru/Tohoku Univ./T.Hayashino et al.); Infrared (NASA/JPL-Caltech/Durham Univ./J.Geach et al.); Right, Illustration: NASA/CXC/M.Weiss

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Astronomers say they’ve discovered the “coming of age” of galaxies and black holes, thanks to new data from NASA’s Chandra X-ray Observatory and other telescopes. The new discovery helps resolve the true nature of gigantic blobs of gas observed around very young galaxies, and sheds light on the formation of galaxies and black holes.

The findings, led by Jim Geach of Durham University in the UK, will appear in the July 10 issue of The Astrophysical Journal.

About a decade ago, astronomers discovered immense reservoirs of hydrogen gas — which they named “blobs” – while conducting surveys of young distant galaxies.  The blobs are glowing brightly in optical light, but the source of immense energy required to power this glow and the nature of these objects were unclear.

Based on the new data and theoretical arguments, Geach and his colleagues show that heating of gas by growing supermassive black holes and bursts of star formation, rather than cooling of gas, most likely powers the blobs. The implication is that blobs represent a stage when the galaxies and black holes are just starting to switch off their rapid growth because of these heating processes.  This is a crucial stage of the evolution of galaxies and black holes – known as “feedback” – and one that astronomers have long been trying to understand.

“We’re seeing signs that the galaxies and black holes inside these blobs are coming of age and are now pushing back on the infalling gas to prevent further growth,” said coauthor Bret Lehmer, also of Durham.  “Massive galaxies must go through a stage like this or they would form too many stars and so end up ridiculously large by the present day.”

Chandra and a collection of other telescopes including Spitzer have observed 29 blobs in one large field in the sky dubbed “SSA22.” These blobs, which are several hundred thousand light years across, are seen when the Universe is only about two billion years old, or roughly 15 percent of its current age.

In five of these blobs, the Chandra data revealed the telltale signature of growing supermassive black holes – a point-like source with luminous X-ray emission. These giant black holes are thought to reside at the centers of most galaxies today, including our own.  Another three of the blobs in this field show possible evidence for such black holes.  Based on further observations, including Spitzer data, the research team was able to determine that several of these galaxies are also dominated by remarkable levels of star formation.

The radiation and powerful outflows from these black holes and bursts of star formation are, according to calculations, powerful enough to light up the hydrogen gas in the blobs they inhabit. In the cases where the signatures of these black holes were not detected, the blobs are generally fainter. The authors show that black holes bright enough to power these blobs would be too dim to be detected given the length of the Chandra observations.

Besides explaining the power source of the blobs, these results help explain their future. Under the heating scenario, the gas in the blobs will not cool down to form stars but will add to the hot gas found between galaxies. SSA22 itself could evolve into a massive galaxy cluster.

“In the beginning the blobs would have fed their galaxies, but what we see now are more like leftovers,” said Geach.  “This means we’ll have to look even further back in time to catch galaxies and black holes in the act of forming from blobs.”

Sources/more information: the Chandra sites at Harvard and NASA.

Super-Size Me: Black Hole Bigger Than Previously Thought

The illustration shows the relationship between the mass of a galaxy’s central black hole and the mass of its central bulge. Credit: Tim Jones/UT-Austin after K. Cordes & S. Brown (STScI)

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Using a new computer model, astronomers have determined that the black hole in the center of the M87 galaxy is at least twice as big as previously thought. Weighing in at 6.4 billion times the Sun’s mass, it is the most massive black hole yet measured, and this new model suggest that the accepted black hole masses in other large nearby galaxies may be off by similar amounts. This has consequences for theories of how galaxies form and grow, and might even solve a long-standing astronomical paradox.

Astronomers Karl Gebhardt from the University of Texas at Austin and Jens Thomas from the Max Planck Institute for Extraterrestrial Physics detailed their findings Monday at the American Astronomical Society conference in Pasadena, California.

To try to understand how galaxies form and grow, astronomers start with basic information about the galaxies today, such as what they are made of, how big they are and how much they weigh. Astronomers measure this last category, galaxy mass, by clocking the speed of stars orbiting within the galaxy.

Studies of the total mass are important, Thomas said, but “the crucial point is to determine whether the mass is in the black hole, the stars, or the dark halo. You have to run a sophisticated model to be able to discover which is which. The more components you have, the more complicated the model is.”

To model M87, Gebhardt and Thomas used one of the world’s most powerful supercomputers, the Lonestar system at The University of Texas at Austin’s Texas Advanced Computing Center. Lonestar is a Dell Linux cluster with 5,840 processing cores and can perform 62 trillion floating-point operations per second. (Today’s top-of-the-line laptop computer has two cores and can perform up to 10 billion floating-point operations per second.)

Gebhardt and Jens’ model of M87 was more complicated than previous models of the galaxy, because in addition to modeling its stars and black hole, it takes into account the galaxy’s “dark halo,” a spherical region surrounding a galaxy that extends beyond its main visible structure, containing the galaxy’s mysterious “dark matter.”

“In the past, we have always considered the dark halo to be significant, but we did not have the computing resources to explore it as well,” Gebhardt said. “We were only able to use stars and black holes before. Toss in the dark halo, it becomes too computationally expensive, you have to go to supercomputers.”

The Lonestar result was a mass for M87’s black hole several times what previous models have found. “We did not expect it at all,” Gebhardt said. He and Jens simply wanted to test their model on “the most important galaxy out there,” he said.

Extremely massive and conveniently nearby (in astronomical terms), M87 was one of the first galaxies suggested to harbor a central black hole nearly three decades ago. It also has an active jet shooting light out the galaxy’s core as matter swirls closer to the black hole, allowing astronomers to study the process by which black holes attract matter. All of these factors make M87 the “the anchor for supermassive black hole studies,” Gebhardt said.

These new results for M87, together with hints from other recent studies and his own recent telescope observations (publications in preparation), lead him to suspect that all black hole masses for the most massive galaxies are underestimated.

That conclusion “is important for how black holes relate to galaxies,” Thomas said. “If you change the mass of the black hole, you change how the black hole relates to the galaxy.” There is a tight relation between the galaxy and its black hole which had allowed researchers to probe the physics of how galaxies grow over cosmic time. Increasing the black hole masses in the most massive galaxies will cause this relation to be re-evaluated.

Higher masses for black holes in nearby galaxies also could solve a paradox concerning the masses of quasars — active black holes at the centers of extremely distant galaxies, seen at a much earlier cosmic epoch. Quasars shine brightly as the material spiraling in, giving off copious radiation before crossing the event horizon (the region beyond which nothing — not even light — can escape).

“There is a long-standing problem in that quasar black hole masses were very large — 10 billion solar masses,” Gebhardt said. “But in local galaxies, we never saw black holes that massive, not nearly. The suspicion was before that the quasar masses were wrong,” he said. But “if we increase the mass of M87 two or three times, the problem almost goes away.”

Today’s conclusions are model-based, but Gebhardt also has made new telescope observations of M87 and other galaxies using new powerful instruments on the Gemini North Telescope and the European Southern Observatory’s Very Large Telescope. He said these data, which will be submitted for publication soon, support the current model-based conclusions about black hole mass.

For future telescope observations of galactic dark haloes, Gebhardt notes that a relatively new instrument at The University of Texas at Austin’s McDonald Observatory is perfect. “If you need to study the halo to get the black hole mass, there’s no better instrument than VIRUS-P,” he said. The instrument is a spectrograph. It separates the light from astronomical objects into its component wavelengths, creating a signature that can be read to find out an object’s distance, speed, motion, temperature, and more.

VIRUS-P is good for halo studies because it can take spectra over a very large area of sky, allowing astronomers to reach the very low light levels at large distances from the galaxy center where the dark halo is dominant. It is a prototype, built to test technology going into the larger VIRUS spectrograph for the forthcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX).

Read the team’s paper.

Sources: AAS, McDonald Observatory

No Nature VS. Nurture for Stars

The Arches Cluster, with young, massive stars, taken by the NACO on ESO’s Very Large Telescope.

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Stars don’t seem to mind where they grow up. Either in a nice quiet neighborhood or in the hellish environment near a supermassive black hole, astronomers were surprised to find the same proportions of low- and high-mass young stars in different types of star forming regions. Using the Very Large Telescope, astronomers snapped one of the sharpest views ever of the Arches Cluster — an extraordinary dense cluster of young stars near the supermassive black hole at the center of the Milky Way. “With the extreme conditions in the Arches Cluster, one might indeed imagine that stars won’t form in the same way as in our quiet solar neighbourhood,” says Pablo Espinoza, the lead author of the paper reporting the new results. “However, our new observations showed that the masses of stars in this cluster actually do follow the same universal law”.

The massive Arches Cluster is located 25 000 light-years away towards the constellation of Sagittarius. It contains about a thousand young, massive stars, less than 2.5 million years old. Astronomers say this region is an ideal laboratory to study how massive stars are born in extreme conditions, as the stars in the cluster experience huge opposing forces from all the activity going on near the supermassive black hole. The Arches Cluster is also ten times heavier than typical young star clusters scattered throughout our Milky Way and is enriched with chemical elements heavier than helium.

The Arches Cluster is located in the centre of the image, but its stars are hidden behind large amount of dust. The bright star at the top of the image is 3 Sagittarii, while the cluster of stars seen at the bottom left is NGC 6451.  Credit: Digitized Sky Survey
The Arches Cluster is located in the centre of the image, but its stars are hidden behind large amount of dust. The bright star at the top of the image is 3 Sagittarii, while the cluster of stars seen at the bottom left is NGC 6451. Credit: Digitized Sky Survey

Using the NACO adaptive optics on the VLT, astronomers were able to take the clearest images yet of the Arches Cluster. Observing the Arches Cluster is very challenging because of the huge quantities of light-absorbing dust between Earth and the Galactic Centre, which visible light cannot penetrate. This is why NACO was used to observe the region in near-infrared light.

The new study confirms the Arches Cluster to be the densest cluster of massive young stars known. It is about three light-years across with more than a thousand stars packed into each cubic light-year — an extreme density a million times greater than in the Sun’s neighborhood.
Astronomers studying clusters of stars have found that higher mass stars are rarer than their less massive brethren, and their relative numbers are the same everywhere, following a universal law.

The astronomers were also able to study the brightest stars in the cluster. “The most massive star we found has a mass of about 120 times that of the Sun,” says co-author Fernando Selman. “We conclude from this that if stars more massive than 130 solar masses exist, they must live for less than 2.5 million years and end their lives without exploding as supernovae, as massive stars usually do.”

The total mass of the cluster seems to be about 30,000 times that of the Sun, much more than was previously thought. “That we can see so much more is due to the exquisite NACO images,” says co-author Jorge Melnick.

Read the team’s paper.

Source: ESO