 |
|
Hubble finds mysterious disk of blue stars around a black hole
September 21, 2005Astronomers using the NASA/ESA Hubble Space Telescope have identified the source of a mysterious blue light surrounding a supermassive black hole in our neighbouring Andromeda Galaxy (M31). Though the light has puzzled astronomers for more than a decade, the new discovery makes the story even more mysterious.
The blue light is coming from a disk of hot, young stars. These stars are whipping around the black hole in much the same way as planets in our solar system are revolving around the Sun. Astronomers are perplexed about how the pancake-shaped disk of stars could form so close to a giant black hole. In such a hostile environment, the black hole's tidal forces should tear matter apart, making it difficult for gas and dust to collapse and form stars. The observations, astronomers say, may provide clues to the activities in the cores of more distant galaxies.
By finding the disk of stars, astronomers also have collected what they say is ironclad evidence for the existence of the monster black hole. The evidence has helped astronomers rule out all alternative theories for the dark mass in the Andromeda Galaxy's core, which scientists have long suspected was a black hole.
"Seeing these stars is like watching a magician pulling a rabbit out of a hat. You know it happened but you don't know how it happened," said Tod Lauer of the National Optical Astronomy Observatory in Tucson, Arizona. He and a team of astronomers, led by Ralf Bender of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and John Kormendy of the University of Texas in Austin, made the Hubble observations. The team's results will be published in the Sept. 20, 2005 issue of the Astrophysical Journal.
Hubble Probes Strange Blue Light Astronomer Ivan King of the University of Washington and colleagues first spotted the strange blue light in 1995 with the Hubble Space Telescope. He thought the light might have come from a single, bright blue star or perhaps from a more exotic energetic process. Three years later, Lauer and Sandra Faber of the University of California at Santa Cruz used Hubble again to study the blue light. Their observations indicated that the blue light was a cluster of blue stars.
Now, new spectroscopic observations by Hubble's Space Telescope Imaging Spectrograph (STIS) reveal that the blue light consists of more than 400 stars that formed in a burst of activity about 200 million years ago. The stars are tightly packed in a disk that is only a light-year across. The disk is nested inside an elliptical ring of older, cooler, redder stars, which was seen in previous Hubble observations.
The astronomers also used STIS to measure the velocities of those stars. They obtained the stars' speeds by calculating how much their light waves are stretched and compressed as they travel around the black hole. Under the black hole's gravitational grip, the stars are travelling very fast: 3.6 million kilometres an hour (1,000 kilometres a second). They are moving so fast that it would take them 40 seconds to circle the Earth and six minutes to arrive at the Moon. The fastest stars complete an orbit in 100 years. Andromeda's active core probably made similar disks of stars in the past and may continue to make them.
"The blue stars in the disk are so short-lived that it is unlikely in the long 12-billion-year history of Andromeda that such a short-lived disk would appear now," Lauer said. "That's why we think that the mechanism that formed this disk of stars probably formed other stellar disks in the past and will trigger them again in the future. We still don't know, however, how such a disk could form in the first place. It still remains an enigma."
The astronomers credit Hubble's superb vision for finding the disk. "Only Hubble has the resolution in blue light to observe this disk," said team member Richard Green of the National Optical Astronomy Observatory in Tucson. "It is so small and so distinct from the surrounding red stars that we were able to use it to probe into the very dynamical heart of Andromeda. These observations were taken by the members of our team that built STIS. We designed its visible channel specifically to seize such an opportunity-to measure starlight closer to a black hole than in any other galaxy outside our own."
Solid Evidence for a Monster Black Hole In addition to the discovery of the disk of stars, the astronomers used this uniquely close look at Andromeda to prove unambiguously that the galaxy hosts a central black hole. In 1988, in independent ground-based studies, John Kormendy and the team of Alan Dressler and Douglas Richstone discovered a central dark object in Andromeda that they believed was a supermassive black hole. This was the first strong case for what are now 40 detections of black holes, most of them made by Hubble. Those observations, however, did not definitively rule out other, very exotic, and far less likely, alternatives.
"There are compelling reasons to believe that these are supermassive black holes," Kormendy said. "But extreme claims require extraordinarily strong evidence. We have to be sure that these are black holes and not dark clusters of dead stars."
The STIS observations of Andromeda are so precise that astronomers have eliminated all other possibilities for what the central, dark object could be. They also calculated that the black hole's mass is 140 million Suns, which is three times more massive than once thought.
So far, dark clusters have definitively been ruled out in only two galaxies, NGC 4258 and our galaxy, the Milky Way. "These two galaxies give us unambiguous proof that black holes exist," Kormendy added. "But both are special cases-NGC 4258 contains a disk of water masers that we observe with radio telescopes, and our galactic center is so close that we can follow individual stellar orbits. Andromeda is the first galaxy in which we can exclude all exotic alternatives to a black hole using Hubble and using the same techniques by which we find almost all supermassive black holes."
"Studying black holes always was a primary mission of Hubble," Kormendy said. "Nailing the black hole in Andromeda is without a doubt an important part of its legacy. It makes us much more confidant that the other central dark objects detected in galaxies are black holes, too."
"Now that we have proven that the black hole is at the centre of the disk of blue stars, the formation of these stars becomes hard to understand," Bender added. "Gas that might form stars must spin around the black hole so quickly-and so much more quickly near the black hole than farther out-that star formation looks almost impossible. But the stars are there."
A Galaxy's Active Core The black hole and the disk of stars are not the only pieces of architecture in Andromeda's core. A team led by Lauer and Faber used Hubble in 1993 to discover that the galaxy appears to have a double cluster of stars at its centre. This finding was a surprise, because two clusters should merge into one in only a few hundred thousand years. Scott Tremaine of Princeton University solved this problem by suggesting that the "double nucleus" was actually a ring of old, red stars. The ring looked like two star clusters because astronomers were only seeing the stars on the opposite ends of the ring. The ring is about five light-years from the black hole and its surrounding disk of blue stars. The disk and the ring are tilted at the same angle as viewed from Earth, suggesting that they may be related.
Although astronomers are surprised to find a blue disk of stars swirling around a supermassive black hole, they also say the puzzling architecture may not be that unusual.
"The dynamics within the core of this neighbouring galaxy may be more common than we think," Lauer explained. "Our own Milky Way apparently has even younger stars close to its own black hole. It seems unlikely that only the closest two big galaxies should have this odd activity. So this behaviour may not be the exception but the rule. And we have found other galaxies that have a double nucleus."
ESA/Hubble Information Centre
"Seeing these stars is like watching a magician pulling a rabbit out of a hat. You know it happened but you don't know how it happened," said Tod Lauer of the National Optical Astronomy Observatory in Tucson, Arizona. He and a team of astronomers, led by Ralf Bender of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, and John Kormendy of the University of Texas in Austin, made the Hubble observations. The team's results will be published in the Sept. 20, 2005 issue of the Astrophysical Journal.
Hubble Probes Strange Blue Light Astronomer Ivan King of the University of Washington and colleagues first spotted the strange blue light in 1995 with the Hubble Space Telescope. He thought the light might have come from a single, bright blue star or perhaps from a more exotic energetic process. Three years later, Lauer and Sandra Faber of the University of California at Santa Cruz used Hubble again to study the blue light. Their observations indicated that the blue light was a cluster of blue stars.
Now, new spectroscopic observations by Hubble's Space Telescope Imaging Spectrograph (STIS) reveal that the blue light consists of more than 400 stars that formed in a burst of activity about 200 million years ago. The stars are tightly packed in a disk that is only a light-year across. The disk is nested inside an elliptical ring of older, cooler, redder stars, which was seen in previous Hubble observations.
The astronomers also used STIS to measure the velocities of those stars. They obtained the stars' speeds by calculating how much their light waves are stretched and compressed as they travel around the black hole. Under the black hole's gravitational grip, the stars are travelling very fast: 3.6 million kilometres an hour (1,000 kilometres a second). They are moving so fast that it would take them 40 seconds to circle the Earth and six minutes to arrive at the Moon. The fastest stars complete an orbit in 100 years. Andromeda's active core probably made similar disks of stars in the past and may continue to make them.
"The blue stars in the disk are so short-lived that it is unlikely in the long 12-billion-year history of Andromeda that such a short-lived disk would appear now," Lauer said. "That's why we think that the mechanism that formed this disk of stars probably formed other stellar disks in the past and will trigger them again in the future. We still don't know, however, how such a disk could form in the first place. It still remains an enigma."
The astronomers credit Hubble's superb vision for finding the disk. "Only Hubble has the resolution in blue light to observe this disk," said team member Richard Green of the National Optical Astronomy Observatory in Tucson. "It is so small and so distinct from the surrounding red stars that we were able to use it to probe into the very dynamical heart of Andromeda. These observations were taken by the members of our team that built STIS. We designed its visible channel specifically to seize such an opportunity-to measure starlight closer to a black hole than in any other galaxy outside our own."
Solid Evidence for a Monster Black Hole In addition to the discovery of the disk of stars, the astronomers used this uniquely close look at Andromeda to prove unambiguously that the galaxy hosts a central black hole. In 1988, in independent ground-based studies, John Kormendy and the team of Alan Dressler and Douglas Richstone discovered a central dark object in Andromeda that they believed was a supermassive black hole. This was the first strong case for what are now 40 detections of black holes, most of them made by Hubble. Those observations, however, did not definitively rule out other, very exotic, and far less likely, alternatives.
"There are compelling reasons to believe that these are supermassive black holes," Kormendy said. "But extreme claims require extraordinarily strong evidence. We have to be sure that these are black holes and not dark clusters of dead stars."
The STIS observations of Andromeda are so precise that astronomers have eliminated all other possibilities for what the central, dark object could be. They also calculated that the black hole's mass is 140 million Suns, which is three times more massive than once thought.
So far, dark clusters have definitively been ruled out in only two galaxies, NGC 4258 and our galaxy, the Milky Way. "These two galaxies give us unambiguous proof that black holes exist," Kormendy added. "But both are special cases-NGC 4258 contains a disk of water masers that we observe with radio telescopes, and our galactic center is so close that we can follow individual stellar orbits. Andromeda is the first galaxy in which we can exclude all exotic alternatives to a black hole using Hubble and using the same techniques by which we find almost all supermassive black holes."
"Studying black holes always was a primary mission of Hubble," Kormendy said. "Nailing the black hole in Andromeda is without a doubt an important part of its legacy. It makes us much more confidant that the other central dark objects detected in galaxies are black holes, too."
"Now that we have proven that the black hole is at the centre of the disk of blue stars, the formation of these stars becomes hard to understand," Bender added. "Gas that might form stars must spin around the black hole so quickly-and so much more quickly near the black hole than farther out-that star formation looks almost impossible. But the stars are there."
A Galaxy's Active Core The black hole and the disk of stars are not the only pieces of architecture in Andromeda's core. A team led by Lauer and Faber used Hubble in 1993 to discover that the galaxy appears to have a double cluster of stars at its centre. This finding was a surprise, because two clusters should merge into one in only a few hundred thousand years. Scott Tremaine of Princeton University solved this problem by suggesting that the "double nucleus" was actually a ring of old, red stars. The ring looked like two star clusters because astronomers were only seeing the stars on the opposite ends of the ring. The ring is about five light-years from the black hole and its surrounding disk of blue stars. The disk and the ring are tilted at the same angle as viewed from Earth, suggesting that they may be related.
Although astronomers are surprised to find a blue disk of stars swirling around a supermassive black hole, they also say the puzzling architecture may not be that unusual.
"The dynamics within the core of this neighbouring galaxy may be more common than we think," Lauer explained. "Our own Milky Way apparently has even younger stars close to its own black hole. It seems unlikely that only the closest two big galaxies should have this odd activity. So this behaviour may not be the exception but the rule. And we have found other galaxies that have a double nucleus."
ESA/Hubble Information Centre
Black Hole News and Current Black Hole Events RSSNew virtual telescope zooms in on Milky Way's super-massive black hole
An international team, led by astronomers at the MIT Haystack Observatory, has obtained the closest views ever of what is believed to be a super-massive black hole at the center of the Milky Way galaxy.
Closest Look Ever at the Edge of a Black Hole
Astronomers have taken the closest look ever at the giant black hole in the center of the Milky Way. By combining telescopes in Hawaii, Arizona, and California, they detected structure at a tiny angular scale of 37 micro-arcseconds - the equivalent of a baseball seen on the surface of the moon, 240,000 miles distant.
Hubble sees magnetic monster in erupting galaxy
The Hubble Space Telescope has found the answer to a long-standing puzzle by resolving giant but delicate filaments shaped by a strong magnetic field around the active galaxy NGC 1275. It is the most striking example of the influence of these immense tentacles of extragalactic magnetic fields, say researchers.
'Cosmic ghost' discovered by volunteer astronomer
When Yale astrophysicist Kevin Schawinski and his colleagues at Oxford University enlisted public support in cataloguing galaxies, they never envisioned the strange object Hanny van Arkel found in archived images of the night sky.
Caltech astronomers describe the bar scene at the beginning of the universe
Bars abound in spiral galaxies today, but this was not always the case. A group of 16 astronomers, led by Kartik Sheth of NASA's Spitzer Science Center at the California Institute of Technology, has found that bars tripled in number over the past seven billion years, indicating that spiral galaxies evolve in shape.
The quiet explosion
A European-led team of astronomers are providing hints that a recent supernova may not be as normal as initially thought. Instead, the star that exploded is now understood to have collapsed into a black hole, producing a weak jet, typical of much more violent events, the so-called gamma-ray bursts.
Polarizing filter allows astronomers to see disks surrounding black holes
For the first time, a team of international researchers has found a way to view the accretion disks surrounding black holes and verify that their true electromagnetic spectra match what astronomers have long predicted they would be.
A new method to weigh giant black holes
How do you weigh the biggest black holes in the universe? One answer now comes from a new and independent technique that UC Irvine scientists and other astronomers have developed using data from NASA's Chandra X-ray Observatory.
UCSB professor's paper on safety of large hadron collider to be published in Physical Review D
Particle colliders creating black holes that could devour the Earth. Sounds like a great Hollywood script.
Radio Telescopes Reveal Unseen Galactic Cannibalism
Radio-telescope images have revealed previously-unseen galactic cannibalism -- a triggering event that leads to feeding frenzies by gigantic black holes at the cores of galaxies. Astronomers have long suspected that the extra-bright cores of spiral galaxies called Seyfert galaxies are powered by supermassive black holes consuming material. However, they could not see how the material is started on its journey toward the black hole.
More Black Hole News Articles
 | The Black Hole War: My Battle with Stephen Hawking to Make the World Safe for Quantum Mechanics by Leonard Susskind What happens when something is sucked into a black hole? Does it disappear? Three decades ago, a young physicist named Stephen Hawking claimed it did-and in doing so put at risk everything we know about physics and the fundamental laws of the universe. Most scientists didn't recognize the import of Hawking's claims, but Leonard Susskind and Gerard t'Hooft realized the threat, and responded with a... |
 | Black Hole by Charles Burns The first issues of Charles Burns's comics series Black Hole began appearing in 1995, and long before it was completed a decade later, readers and fellow artists were speaking of it in tones of awe and comparing it to recent classics of the form like Chris Ware's Jimmy Corrigan and Daniel Clowes's Ghost World. Burns is the sort of meticulous, uncompromising artist whom other artists speak of with... |
 | Death by Black Hole: And Other Cosmic Quandaries by Neil deGrasse Tyson "One of today's best popularizers of science."—Kirkus ReviewsLoyal readers of the monthly "Universe" essays in Natural History magazine have long recognized Neil deGrasse Tyson's talent for guiding them through the mysteries of the cosmos with stunning clarity and childlike enthusiasm. Here Tyson compiles his favorite essays across a myriad of cosmic topics. The title essay introduces... |
 | Radical Amazement: Contemplative Lessons from Black Holes, Supernovas, And Other Wonders of the Universe by Judy Cannato |
 | An Introduction To Black Holes, Information And The String Theory Revolution: The Holographic Universe by Leonard Susskind, James Lindesay Over the last decade the physics of black holes has been revolutionized by developments that grew out of Jacob Bekenstein s realization that black holes have entropy. Stephen Hawking raised profound issues concerning the loss of information in black hole evaporation and the consistency of quantum mechanics in a world with gravity. For two decades these questions puzzled theoretical physicists and... |
 | Black Holes and Time Warps: Einstein's Outrageous Legacy (Commonwealth Fund Book Program) by Kip S. Thorne |
 | Everyone Worth Knowing by Lauren Weisberger Lauren Weisberger, whose bestselling debut The Devil Wears Prada outed the vicious antics of the magazine industry elite, is back at it with Everyone Worth Knowing, another cautionary tale of sex, power, and fame. This time around, the PR industry is her target, and Prada fans will recognize similar themes throughout this entertaining, if at times overly dramatic, exposé. Bette Robinson is a... |
 | Exploring Black Holes: Introduction to General Relativity by Edwin F. Taylor, John Archibald Wheeler |
 | Introducing Einstein's Relativity by R. d'Inverno There is little doubt that Einstein's theory of relativity captures the imagination. It is unrivalled in forming the basis of the way we view the universe and the many surprises that the theory has in store -- the characteristics of black holes, the prospect of detecting gravitational waves, and the sheer scope and profundity of current cosmology excite all students of relativity. The aim of this... |
 | Decoding the Universe: How the New Science of Information Is Explaining Everything in the Cosmos, from Our Brains to Black Holes by Charles Seife The author of Zero explains the scientific revolution that is transforming the way we understand our world Previously the domain of philosophers and linguists, information theory has now moved beyond the province of code breakers to become the crucial science of our time. In Decoding the Universe, Charles Seife draws on his gift for making cutting-edge science accessible to explain how this new... |
| © 2008 BrightSurf.com |