Category: Black Holes

Hubble image from a sample of 20 nearby quasars. Image credit: NASA/ESA/ESO Click to enlarge
The detection of a super-massive black hole without a massive ‘host’ galaxy is the surprising result from a large Hubble and VLT study of quasars.

This is the first convincing discovery of such an object. One intriguing explanation is that the host galaxy may be made almost exclusively of ‘dark matter’.
A team of European astronomers has used two of the most powerful astronomical facilities available, the NASA/ESA Hubble Space Telescope and the ESO Very Large Telescope (VLT) at Cerro Paranal, to discover a bright quasar without a massive host galaxy.

Quasars are powerful and typically very distant source of huge amounts of radiation. They are commonly associated with galaxies containing an active central black hole.

The team conducted a detailed study of 20 relatively nearby quasars. For 19 of them, they found, as expected, that these super-massive black holes are surrounded by a host galaxy. But when they studied the bright quasar HE0450-2958, located some 5000 million light-years away, they could not find evidence for a host galaxy.

The astronomers suggest that this may indicate a rare case of a collision between a seemingly normal spiral galaxy and an ‘exotic’ object harbouring a very massive black hole.

With masses that are hundreds of millions times bigger than the Sun, super-massive black holes are commonly found in the centres of the most massive galaxies, including our own Milky Way. These black holes sometimes dramatically manifest themselves by devouring matter that they gravitationally swallow from their surroundings.

The best fed of these objects shine as ‘quasars’ (standing for ‘quasi-stellar object’ because they had initially been thought of as stars).

The past decade of observations, largely with the Hubble telescope, has shown that quasars are normally associated with massive host galaxies. However, observing the host galaxy of a quasar is challenging work because the quasar completely outshines the host and masks the galaxy?s underlying structure.

To overcome this problem, the astronomers devised a new and highly efficient strategy. Combining Hubble?s ultra-sharp images and spectroscopy from ESO?s VLT, they observed their sample of 20 quasars at the same time as a reference star. The star served as a reference pinpoint light source that was used to disentangle the quasar light from any possible light from an underlying galaxy.

Despite the innovative techniques used, no host galaxy was seen around HE0450-2958. This means that if any host galaxy exists, it must either be at least six times fainter than typical host galaxies, or have a radius smaller than about 300 light-years, i.e. 20 to 170 times smaller than typical host galaxies (which normally have radii ranging from about 6000 to 50 000 light-years).

“With the powerful combination of Hubble and the VLT we are confident that we would have been able to detect a normal host galaxy,” said Pierre Magain of the Universit? de Li?ge, Belgium.

The astronomers did however detect an interesting smaller cloud of gas about 2500 light-years wide near the quasar, which they call ‘the blob’. VLT observations show this cloud to be glowing because it is bathed in the intense radiation coming from the quasar, and not from stars inside the cloud. Most likely, it is the gas from this cloud that feeds the super-massive black hole, thereby allowing it to become a quasar.

“The absence of a massive host galaxy, combined with the existence of the blob and the star-forming galaxy, lead us to believe that we have uncovered a really exotic quasar,” said Fr?d?ric Courbin of the Ecole Polytechnique Federale de Lausanne, Switzerland.

“There is little doubt that an increase in the formation of stars in the companion galaxy and the quasar itself have been ignited by a collision that must have taken place about 100 million years ago. What happened to the putative quasar host remains unknown.”

HE0450-2958 is a challenging case. The astronomers propose several possible explanations. Has the host galaxy been completely disrupted as a result of the collision? Has an isolated black hole captured gas while crossing the disk of a spiral galaxy? This would require very special conditions and would probably not have caused such a tremendous disturbance of the neighbouring galaxy as is observed. Further studies will hopefully clarify the situation.

Another intriguing hypothesis is that the galaxy harbouring the black hole was almost exclusively made of ‘dark matter’. It may be that what is observed is a normal phase in the formation of a massive galaxy, which in this case has taken place several 1000 million years later than in most others.

Original Source: ESA Portal

GRB 050509B, detected on 9 May 2005, was a *very* short burst, lasting just 30 milliseconds. Image credit: NASA/JPL. Click to enlarge.
After 30 years, they finally caught one. Scientists on Monday have for the first time detected and pinned down the location of a so-called “short” gamma-ray burst, lasting only 50 milliseconds.

The burst marks the birth of a black hole. The astronomy community is buzzing with speculation on what could have caused the burst, perhaps a collision of two older black holes or two neutron stars. A multitude of follow-up observations are planned; the answer might come in a few more days. “Everything about this gamma-ray burst so far supports the merger theory,” said Steinn Sigurdsson, associate professor of astronomy and astrophysics at Penn State and a gamma-ray-burst theorist.

Gamma-ray bursts are the most powerful explosions known in the universe. Recently, the longer ones — lasting more than two seconds — have become easy prey for NASA satellites such as Swift, built to detect and quickly locate the flashes. Short bursts had remained elusive until Monday, when Swift detected one, autonomously locked onto a location, and focused its onboard telescopes in less than a minute to capture the burst afterglow.

“Seeing the afterglow from a ‘short’ gamma-ray burst was a major goal for Swift, and we hit it just a few months after launch,” said Neil Gehrels, Swift project scientist at NASA Goddard Space Flight Center in Greenbelt, Maryland. “Now, for the first time, we have real data to figure out what these things are.”

Like clues left at a crime scene, the afterglow contains information about what caused the burst. Most scientists are convinced short and long bursts arise from two different catastrophic origins. The longer bursts appear to be from massive star explosions in very distant galaxies. The shorter ones — less than two seconds and often just a few milliseconds — are the deeper mystery because they have been simply too fast to observe in detail.

The Monday burst is called GRB 050509B. Swift’s X-ray Telescope detected a weak afterglow that faded away after about five minutes. Swift’s Ultraviolet/Optical Telescope did not see an afterglow. Ground-based telescopes have not yet definitely detected an afterglow either. In contrast, afterglows from long bursts linger from days to weeks.

All of this fits the pattern of a collision between some combination of black holes or neutron stars, both of which are created in the death of massive stars. Neutron stars are dense spheres about 20 miles across. Black holes have no surface and are regions in space of infinite density. Theory predicts that these kinds of collisions wouldn’t produce a long afterglow because there isn’t much “fuel” — such as dust and gas — from the objects and in the region to sustain an afterglow.

GRB 050509B appears to have occurred near an unusual galaxy that has old stars and is relatively nearby–about 2.7 billion light years away–which also is consistent with the theory that short bursts come from older, evolved neutron stars and black holes. In contrast, longer gamma-ray bursts tend to be in young, distant galaxies filled with young, massive stars — remnants of the early universe.

“We are combing the region around the burst with the Keck Telescope for clues about this burst or its host galaxy,” said Shri Kulkarni, a gamma-ray burst expert at Caltech. “What we are seeing so far is what proponents of the merger theory have been saying all along.” Such an evanescent afterglow has been expected in the most popular model for short hard bursts to date. Additional observations are planned for NASA’s Hubble Space Telescope and Chandra X-ray Observatory.

Swift is a NASA mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council, United Kingdom; and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities, and international partners, including Penn State University; Los Alamos National Laboratory in New Mexico; Sonoma State University in Rohnert Park, California; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester in England; Brera Observatory in Milan, Italy; and ASI Science Data Center in Frascati, Italy. For more information about this and other Swift-detected bursts, refer to http://grb.sonoma.edu.

Original Source: Eberly College News Release

Image credit: ESA
Contrary to established scientific thinking, you’d be roasted and not “spaghettified” if you stumbled into a supermassive black hole. New research being presented at the Institute of Physics conference Physics 2005 in Warwick will take a new look at the diet of the universe’s most intriguing object, black holes.

Black holes stand at the very edge of scientific theory. Most scientists believe they exist, although many of their theories break down under the extreme conditions within. But Professor Andrew Hamilton of the University of Colorado says he knows what you would find inside, and challenges the traditional idea that gravity would cause you death by “spaghettification”.

Most people have heard of the event horizon of a black hole, as the point of no return. But astronomically realistic black holes are more complex and should have two horizons, an outer and an inner. In the bizarre physics of black holes, time and space are exchanged when you cross an event horizon, but at a second horizon they would switch back again.

Traveling into a black hole, you would therefore pass through a strange region where space is falling inward faster than light, before finally entering a zone of normal space at the core. It’s this core of normal space which Professor Hamilton has been working on.

A so-called singularity sits at the centre of the core, swallowing up matter. But according to Professor Hamilton, the strange laws of general relativity temper its appetite. If the singularity ate too quickly, it would become gravitationally repulsive, so instead, matter piles up in a hot, dense plasma filling the core of the black hole and siphoning gradually into the singularity.

Depending on the size of the black hole, this plasma could be the cause of a space traveller’s demise. Most books will tell you that under the extreme gravitational conditions of a black hole, your feet would experience gravity more strongly than your head, and your body would be stretched out like spaghetti.

For a small black hole with the mass of several suns, this should still be true. But for a supermassive black hole weighing millions or billions of suns, explains Professor Hamilton, the tidal forces which cause spaghettification are relatively weak. You would instead be roasted by the heat of the plasma.

Professor Andrew Hamilton is Professor of Astrophysics at the Department of Astrophysical and Planetary Sciences, University of Colorado.

Original Source: Institute of Physics News Release

The whole sky is filled with a diffuse, high energy glow: the cosmic X-ray background. In the last years the astronomers could show, that this radiation can almost completely be associated with individual objects. Similarly, Galileo Galilei in the beginning of the 17th century resolved the light of the Milky Way into individual stars. The X-ray background originates in hundreds of millions of supermassive Black Holes, which feed from matter in the centres of distant galaxy systems. Because the Black Holes are accreting mass, we observe them in the X-ray background during their growth phase. In today’s Universe, massive Black Holes are found in the centres of practically all nearby galaxies.

When matter rushes down the abyss of a Black Hole, it speeds around the cosmic maelstrom almost with the velocity of light and is heated up so strongly, that it emits its “last cry of help” in the form of high energy radiation, before it vanishes forever. Therefore the putatively invisible Black Holes are among the most luminous objects in the universe, if they are fed well in the centres of so called active galaxies. The chemical cal elements in the matter emit X-rays of a characteristic wavelength and can therefore be identified through their spectral fingerprint. Atoms of the element iron are a particularly useful diagnostic tool, because this metal is most abundant in the cosmos and radiates most intensely at high temperatures.

In a way similar to the radar traps, with which the police identifies speeding cars, the relativistic speeds of iron atoms circling the Black Hole can be measured through a shift in wavelength of their light. Through a combination of the effects predicted by Einstein’s special and general theory of relativity, however, a characteristically broadened, asymmetric line profile, i.e. a smeared fingerprint is expected in the X-ray light of Black Holes. Special relativity postulates that moving clocks run slow, and general relativity predicts that clocks run slow in the vicinity of large masses. Both effects lead to a shift of the light emitted by iron atoms into the longer wavelength part of the electromagnetic spectrum. However, if we observe the matter circling in the so called “accretion disk” (Fig. 1) from the side, the light from atoms racing towards us appears shifted to shorter wavelengths and much brighter than that moving away from us. These effects of Relativity are stronger, the closer the matter reaches to the black hole. Because of the curved spacetime they are strongest in fast rotating Black Holes. In the past years, measurements of relativistic iron lines have been possible in a few nearby galaxies – for the first time in 1995 with the Japanese ASCA satellite.

Now the researchers around G?nther Hasinger of the Max-Planck-Institute for extraterrestrial Physics, jointly with the group of Xavier Barcons at the Spanish Instituto de F?sica de Cantabria in Santander and Andy Fabian at the Institute of Astronomy in Cambridge, UK have uncovered the relativistically smeared fingerprint of iron atoms in the average X-ray light of about 100 distant Black Holes of the X-ray background (Fig. 2). The astrophysicists utilized the X-ray observatory XMM-Newton of the European Space Agency ESA. They pointed the instrument to a field in the Big Dipper constellation for more than 500 hours and discovered several hundred weak X-ray sources.

Because of the expansion of the Universe the galaxies move away from us with a speed increasing with their distance and thus their spectral lines all appear at different wavelength; the astronomers had first to correct the X-ray light of all objects into the rest frame of the Milky Way. The necessary distance measurements for more than 100 objects were obtained with the American Keck-Telescope. After having co-added the light from all objects, the researchers were very surprised about the unexpectedly large signal and the characteristically broadened shape of the iron line.

From the strength of the signal they deduced the fraction of iron atoms in the accreted matter. Surprisingly, the chemical abundance of iron in the “nutrition” of these relatively young Black Holes is about three times higher than in our Solar system, which had been created significantly later. The centres of galaxies in the early Universe therefore must have had a particularly efficient method to produce iron, possibly because violent star forming activity “breeds” the chemical elements rather quickly in active galaxies. The width of the line indicated that the iron atoms must radiate rather close to the black hole, consistent with rapidly spinning Black Holes. This conclusion is also found indirectly by other groups, who compared the energy in the X-ray background with the total mass of “dormant” Black Holes in nearby galaxies.

Original Source: Max Planck Society News Release

Want to update your computer desktop background? Here are some black background pictures.

The very largest black holes reach a certain point and then grow no more, according to the best survey to date of black holes made with NASA’s Chandra X-ray Observatory. Scientists have also discovered many previously hidden black holes that are well below their weight limit.

These new results corroborate recent theoretical work about how black holes and galaxies grow. The biggest black holes, those with at least 100 million times the mass of the Sun, ate voraciously during the early Universe. Nearly all of them ran out of ‘food’ billions of years ago and went onto a forced starvation diet.

Focus on Black Holes in the Chandra Deep Field North Focus on Black Holes in the Chandra Deep Field North
On the other hand, black holes between about 10 and 100 million solar masses followed a more controlled eating plan. Because they took smaller portions of their meals of gas and dust, they continue growing today.

“Our data show that some supermassive black holes seem to binge, while others prefer to graze”, said Amy Barger of the University of Wisconsin in Madison and the University of Hawaii, lead author of the paper describing the results in the latest issue of The Astronomical Journal (Feb 2005). “We now understand better than ever before how supermassive black holes grow.”

One revelation is that there is a strong connection between the growth of black holes and the birth of stars. Previously, astronomers had done careful studies of the birthrate of stars in galaxies, but didn’t know as much about the black holes at their centers.

“These galaxies lose material into their central black holes at the same time that they make their stars,” said Barger. “So whatever mechanism governs star formation in galaxies also governs black hole growth.”

Astronomers have made an accurate census of both the biggest, active black holes in the distance, and the relatively smaller, calmer ones closer by. Now, for the first time, the ones in between have been counted properly.

Growth of the Biggest Black Holes Illustrated Growth of the Biggest Black Holes Illustrated
“We need to have an accurate head count over time of all growing black holes if we ever hope to understand their habits, so to speak,” co-author Richard Mushotzky of NASA’s Goddard Space Flight Center in Greenbelt, Md.

Supermassive black holes themselves are invisible, but heated gas around them — some of which will eventually fall into the black hole – produces copious amounts of radiation in the centers of galaxies as the black holes grow.

This study relied on the deepest X-ray images ever obtained, the Chandra Deep Fields North and South, plus a key wider-area survey of an area called the “Lockman Hole”. The distances to the X-ray sources were determined by optical spectroscopic follow-up at the Keck 10-meter telescope on Mauna Kea in Hawaii, and show the black holes range from less than a billion to 12 billion light years away.

Since X-rays can penetrate the gas and dust that block optical and ultraviolet emission, the very long-exposure X-ray images are crucial to find black holes that otherwise would go unnoticed.

Chandra found that many of the black holes smaller than about 100 million Suns are buried under large amounts of dust and gas, which prevents detection of the optical light from the heated material near the black hole. The X-rays are more energetic and are able to burrow through this dust and gas. However, the largest of the black holes show little sign of obscuration by dust or gas. In a form of weight self-control, powerful winds generated by the black hole’s feeding frenzy may have cleared out the remaining dust and gas.

Other aspects of black hole growth were uncovered. For example, the typical size of the galaxies undergoing supermassive black hole formation reduces with cosmic time. Such “cosmic downsizing” was previously observed for galaxies undergoing star formation. These results connect well with the observations of nearby galaxies, which find that the mass of a supermassive black hole is proportional to the mass of the central region of its host galaxy.

The other co-authors on the paper in the February 2005 issue of The Astronomical Journal were Len Cowie, Wei-Hao Wang, and Peter Capak (Institute for Astronomy, Univ. of Hawaii), Yuxuan Yang (GSFC and the Univ. of Maryland, College Park), and Aaron Steffan (Univ. of Wisconsin, Madison).

NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Space Mission Directorate, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at: http://chandra.harvard.edu and http://chandra.nasa.gov

Original Source: Chandra News Release

The NASA-led Swift mission has detected and imaged its first gamma-ray burst, likely the birth cry of a brand new black hole.

The bright and long burst occurred on January 17. It was in the midst of exploding, as Swift autonomously turned to focus in less than 200 seconds. The satellite was fast enough to capture an image of the event with its X-Ray Telescope (XRT), while gamma rays were still being detected with the Burst Alert Telescope (BAT).

“This is the first time an X-ray telescope has imaged a gamma-ray burst, while it was bursting,” said Dr. Neil Gehrels, Swift’s Principal Investigator at NASA’s Goddard Space Flight Center, Greenbelt, Md. “Most bursts are gone in about 10 seconds, and few last upwards of a minute. Previous X-ray images have captured the burst afterglow, not the burst itself.”

“This is the one that didn’t get away,” said Prof. John Nousek, Swift’s Mission Operations Director at Penn State University, State College, Pa. “And this is what Swift was built to do: to detect these fleeting gamma-ray bursts and focus its telescopes on them autonomously within about a minute. The most exciting thing is this mission is just revving up.”

Swift has three main instruments. The BAT detects bursts and initiates the autonomous slewing to bring the XRT and the Ultraviolet/Optical Telescope (UVOT) within focus of the burst. In December the BAT started detecting bursts, including a remarkable triple detection on December 19. Today’s announcement marks the first BAT detection autonomously followed by XRT detection, demonstrating the satellite is swiftly slewing as planned. The UVOT is still being tested, and it was not collecting data when the burst was detected.

Scientists will need several weeks to fully understand this burst, GRB050117, so named for the date of detection. Telescopes in orbit and on Earth will turn to the precise burst location provided by Swift to observe the burst afterglow and the region surrounding the burst.

“We are frantically analyzing the XRT data to understand the X-ray emission seen during the initial explosion and the very early afterglow,” said Dr. David Burrows, the XRT lead at Penn State. “This is a whole new ballgame. No one has ever imaged X-rays during the transition of a gamma-ray burst from the brilliant flash to the fading embers.”

When the UVOT is fully operational, both the XRT and UVOT will provide an in-depth observation of the gamma-ray burst and its afterglow. The burst is gone in a flash, but scientists can study the afterglow to learn about what caused the burst, much like a detective hunts for clues at a crime scene.

The origin of gamma-ray bursts remains a mystery. At least some appear to originate in massive star explosions. Others might be the result of merging black holes or neutron stars. Any of these scenarios likely will result in the formation of a new black hole.

Several of these bursts occur daily somewhere in the visible universe. No prompt X-ray emission (coincident with the gamma-ray burst) has been previously imaged, because it usually takes hours to turn an X-ray telescope towards a burst. Scientists expect Swift to be fully operational by February 1.

Swift, still in its checkout phase, is an international collaboration launched on November 20, 2004. It is a NASA mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council, United Kingdom.

The spacecraft was built in collaboration with national laboratories, universities and international partners, including Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; Brera Observatory in Milan; and ASI Science Data Center in Frascati, Italy.

For more information about Swift on the Web, visit:

http://www.nasa.gov/swift

Original Source: NASA News Release

NASA’s Chandra X-ray Observatory has obtained definitive evidence that a distant quasar formed less than a billion years after the Big Bang contains a fully-grown supermassive black hole generating energy at the rate of twenty trillion Suns. The existence of such massive black holes at this early epoch of the Universe challenges theories of the formation of galaxies and supermassive black holes.

Astronomers Daniel Schwartz and Shanil Virani of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA observed the quasar, known as SDSSp J1306, which is 12.7 billion light years away. Since the Universe is estimated to be 13.7 billion years old, we see the quasar as it was a billion years after the Big Bang. They found that the distribution of X-rays with energy, or X-ray spectrum, is indistinguishable from that of nearby, older quasars. Likewise, the relative brightness at optical and X-ray wavelengths of SDSSp J1306 was similar to that of the nearby group of quasars. Optical observations suggest that the mass of the black hole is about a billion solar masses.

Evidence of another early-epoch supermassive black hole was published previously by a team of scientists from the California Institute of Technology and the United Kingdom using the XMM-Newton X-ray satellite. They observed the quasar SDSSp J1030 at a distance of 12.8 billion light years and found essentially the same result for the X-ray spectrum as the Smithsonian scientists found for SDSSp J1306. Chandra’s precise location and spectrum for SDSSp J1306 with nearly the same properties eliminate any lingering uncertainty that precocious supermassive black holes exist.

“These two results seem to indicate that the way supermassive black holes produce X-rays has remained essentially the same from a very early date in the Universe,” said Schwartz. “This implies that the central black hole engine in a massive galaxy was formed very soon after the Big Bang.”

There is general agreement among astronomers that X-radiation from the vicinity of supermassive black holes is produced as gas is pulled toward a black hole, and heated to temperatures ranging from millions to billions of degrees. Most of the infalling gas is concentrated in a rapidly rotating disk, the inner part of which has a hot atmosphere or corona where temperatures can climb to billions of degrees.

Although the precise geometry and details of the X-ray production are not known, observations of numerous quasars, or supermassive black holes, have shown that many of them have very similar X-ray spectra, especially at high X-ray energies. This suggests that the basic geometry and mechanism are the same for these objects.

The remarkable similarity of the X-ray spectra of the young supermassive black holes to those of much older ones means that the supermassive black holes and their accretion disks, were already in place less than a billion years after the Big Bang. One possibility is that millions of 100 solar mass black holes formed from the collapse of massive stars in the young galaxy, and subsequently built up a billion-solar mass black hole in the center of the galaxy through mergers and accretion of gas.

To answer the question of how and when supermassive black holes were formed, astronomers plan to use the very deep Chandra exposures and other surveys to identify and study quasars at even earlier ages.

The paper by Schwartz and Virani on SDSSp J1306 was published in the November 1, 2004 issue of The Astrophysical Journal. The paper by Duncan Farrah and colleagues on SDSS J1030 was published in the August 10, 2004 issue of The Astrophysical Journal.

Chandra observed J1306 with its Advanced CCD Imaging Spectrometer (ACIS) instrument for approximately 33 hours in November 2003. NASA’s Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for NASA’s Office of Space Science, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Additional information and images are available at:
http://chandra.harvard.edu and http://chandra.nasa.gov

Original Source: Chandra News Release

Using archived science verification data from the Hokupa?a/QUIRC Adaptive Optics system on Gemini North, a French/US team of astronomers led by Jean-Pierre Maillard of the Institut d?Astrophysique de Paris has confirmed the physical association of a cluster of massive stars in the infrared source IRS 13 near the center of the Milky Way galaxy.

The team also used data from Hubble Space Telescope, the Chandra X-Ray Observatory, the Canada-France-Hawai?i Telescope (CFHT), and the Very Large Array to provide broad spectral coverage to complement the Gemini data. The Gemini observations consisted of deconvolved H and Kp band images that identified the existence of two formerly undetected sources within IRS 13E. In all, seven individual massive stars appear to be associated with what the team believes was once a larger cluster of massive stars held together by a central intermediate-mass black hole of about 1,300 solar masses. (This black hole is distinct from the black hole at the galactic center which has a mass of about four million solar masses.) The seven individual stars of IRS 13E seen within a diameter of about 0.5″ (or projected 0.6 light-year across) are co-moving westward with a similar velocity of about 280 kilometers per second in the plane of the sky.

The compactness of the cluster and the common proper motion of the components suggest that they are kept together by a massive source, a stellar black hole at the center of IRS 13E. The size of the cluster allow to infer a mean orbit radius. The radial velocities (+/- 30 kilometers per second) of the individual stars derived from the BEAR Fourier Transform Spectrometer (CFHT) measurements can be used to estimate the average orbital velocity. The authors then explored a range of orbital assumptions and were able to constraint the mass of the holding black hole to about 1,300 solar masses rather robustly.

The team also speculates that this cluster was once located farther from the galactic center, where the stars could form away from the extreme gravitational influence of the central supermassive black hole. IRS 13E seems to be the wreckage or remnant core of a once larger cluster of stars that is now spiraling towards Sgr A* at the galactic center.

This theory also explains the existence of other massive stars around the galactic center, which are thought to be stars stripped from the cluster due to the gravitational environment around the galaxy?s central black hole.

The Gemini data for this work were obtained by a team led by Francois Rigaut (Gemini Observatory) as part of an adaptive optics demonstration run in July 2000. The results are published in Astronomy and Astrophysics, Volume 423, pgs 155-167 (2004)

Original Source: Gemini News Release

Image credit: Harvard CfA
Most galaxies, including the Milky Way, are filled with giant clouds of gas and dust called nebulae that appear as dark silhouettes against the starry background. Nebulae shine only when illuminated or excited by nearby energy sources.

Usually, the energy source is one or more stars. But today at the 204th meeting of the American Astronomical Society in Denver, Colorado, Smithsonian astrophysicist Philip Kaaret (Harvard-Smithsonian Center for Astrophysics) announced that one nebula is illuminated by X-rays from a black hole. Moreover, the brightness of the nebula suggests that the X-ray source may be an intermediate-mass black hole many times larger than most stellar black holes.

This surprising find offers only the second known example of a black hole-illuminated nebula, after LMC X-1 in the Large Magellanic Cloud, and the first example of a nebula powered by an intermediate-mass black hole.

“Astronomers always get excited about new things, and this nebula is certainly something new. Finding it is like getting a royal flush the first time you play poker – it’s that rare,” said Kaaret.

Initially discovered by Manfred Pakull and Laurent Mirioni (University of Strasbourg), the nebula is located 10 million light-years away in the dwarf irregular galaxy Holmberg II. Two years ago, Pakull and Mirioni noted that it seemed to be associated with an ultraluminous X-ray source.

By combining observations from NASA’s Hubble Space Telescope and Chandra X-ray Observatory with those from ESA’s XMM-Newton spacecraft, Kaaret and his colleagues, Martin Ward (University of Leicester) and Andreas Zezas (CfA), pinpointed the X-ray source at the center of the nebula. Moreover, the mystery source is pouring out X-rays at a tremendous rate, shining one million times brighter in X-rays than the Sun shines at all wavelengths of light combined.

The observations by Kaaret and his associates indicate that those X-rays are generated by a black hole gobbling matter from a young, massive companion star at a rate of about one Earth mass every four years. That modest accretion rate is sufficient to ionize and light up a huge 100-light-year-wide swath of the surrounding nebula.

The X-ray emissions provide an important clue to the nature of the black hole. Some astronomers have suggested that X-rays from the source in Holmberg II and similar bright sources are beamed in the Earth’s direction like a searchlight. Such beaming would make the X-ray source appear brighter than it really is, thereby making the black hole appear more massive than it really is.

Kaaret’s data contradict that view, showing instead that the black hole in Holmberg II sends out X-rays evenly in all directions. Therefore, its brightness suggests that it must be more massive than any stellar black hole in our own Galaxy, weighing in at more than 25 times the mass of the Sun and likely more than 40 solar masses. That would rank it as an “intermediate-mass” black hole.

“It’s not easy to explain how intermediate-mass black holes form. Since we only have a few examples to study, every new find is important,” said Kaaret.

This research will be published in a paper co-authored by Kaaret, Ward and Zezas in an upcoming issue of the Monthly Notices of the Royal Astronomical Society.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: Harvard CfA News Release

Image credit: ESA
A European team has used the Astrophysical Virtual Observatory (AVO) to find 30 supermassive black holes that had previously escaped detection behind masking dust clouds. The identification of this large population of long-sought ?hidden? black holes is the first scientific discovery to emerge from a Virtual Observatory. The result suggests that astronomers may have underestimated the number of powerful supermassive black holes by as much as a factor of five.

Black holes collect dust. They lurk at the centres of active galaxies in environments not unlike those found in violent tornadoes on Earth. Just as in a tornado, where debris is often found spinning about the vortex, so in a black hole, a dust torus surrounds its waist. In some cases astronomers can look along the axis of the dust torus from above or from below and have a clear view of the black hole. Technically these objects are then called ?type 1 sources?. ?Type 2 sources? lie with the dust torus edge-on as viewed from Earth so our view of the black hole is totally blocked by the dust over a range of wavelengths from the near-infrared to soft X-rays.

While many dust-obscured low-power black holes (called ?Seyfert 2s?) have been identified, until recently few of their high-power counterparts were known. The identification of a population of high-power obscured black holes and the active galaxies in which they live has been a key goal for astronomers and will lead to greater understanding and a refinement of the cosmological models describing our Universe.

The European AVO science team led by Paolo Padovani from Space Telescope-European Coordinating Facility and the European Southern Observatory in Munich, Germany, now announces the discovery of a whole population of the obscured, powerful supermassive black holes. Thirty of these objects were found in the so-called GOODS (Great Observatories Origins Deep Survey) fields. The GOODS survey consists of two areas that include some of the deepest observations from space- and ground-based telescopes, including the NASA/ESA Hubble Space Telescope, and have become the best studied patches in the sky.

Padovani and the team used an innovative technique. Using a Virtual Observatory (VO) they combined information from multiple wavelengths from Hubble, ESO?s Very Large Telescope and NASA’s Chandra. This unprecedented team effort by the largest telescopes in the world made this discovery possible. The majority of the sources are so faint that it is currently not possible to take spectra of them and the VO techniques made it possible for the researchers to work seamlessly with images and catalogues from many different sources.

According to Paolo Padovani: ?This discovery means that surveys of powerful supermassive black holes have so far underestimated their numbers by at least a factor of two, and possibly by up to a factor of five.?

The paper describing these results has just been accepted by the European journal Astro?nomy & Astrophysics and will be published in an upcoming issue. This is the first refereed scientific paper based on end-to-end use of Virtual Observatory tools. The results in the paper show that the VO has evolved beyond the demonstration level to become a real research tool.

The European Astrophysical Virtual Observatory (AVO), funded partly by the European Commission, is the specific VO used for this project. With this work AVO demonstrates cutting-edge science by giving astronomers easy access to manipulation of image and catalogue data on remote computer networks. Until now objects were normally identified by taking a spectrum with a telescope, but now science is moving into an era where objects are pinpointed efficiently by using easily accessible multiwavelength information.

“These discoveries highlight the kind of scientific impact that Virtual Observatory technologies and standards will have on astronomy world-wide”, said Peter Quinn (European Southern Observatory), director of the AVO. “The Astrophysical Virtual Observatory wants to continue to work with astronomers in Europe to enable more discoveries like this, using combined data from ground- and space-based observatories”.

The team already has plans to investigate the new population of dusty black holes by using even more telescopes: the European Southern Observatory?s Very Large Telescope (near-infrared), NASA?s Spitzer Space Telescope (far-infrared) using emerging new VO tools. This will give further insight into the nature of these sources.

Original Source: ESA News Release