Virtual Trips to Black Holes and Neutron Stars
Black Hole Simulations
Stephen Hawking's Homepage
Project Milagro Looks for High-Energy Cosmic Rays
Numerical Relativity Group
"The Black Hole in the Galactic Center" a slideshow by Heino Falcke
Thanks to two orbiting X-ray observatories, astronomers have the first strong evidence of a supermassive black hole ripping apart a star and consuming a portion of it.
The event, captured by NASA's Chandra and ESA's XMM-Newton X- ray Observatories, had long been predicted by theory, but never confirmed.
Astronomers believe a doomed star came too close to a giant black hole after being thrown off course by a close encounter with another star. As it neared the enormous gravity of the black hole, the star was stretched by tidal forces until it was torn apart. This discovery provides crucial information about how these black holes grow and affect surrounding stars and gas.
"Stars can survive being stretched a small amount, as they are in binary star systems, but this star was stretched beyond its breaking point," said Stefanie Komossa of the Max Planck Institute for Extraterrestrial Physics (MPE) in Germany, leader of the international team of researchers. "This unlucky star just wandered into the wrong neighborhood."
While other observations have hinted stars are destroyed by black holes (events known as "stellar tidal disruptions"), these new results are the first strong evidence. Evidence already exists for supermassive black holes in many galaxies, but looking for tidal disruptions represents a completely independent way to search for black holes. Observations like these are urgently needed to determine how quickly black holes can grow by swallowing neighboring stars.
Observations with Chandra and XMM-Newton, combined with earlier images from the German Roentgen satellite, detected a powerful X-ray outburst from the center of the galaxy RXJ1242-11. This outburst, one of the most extreme ever detected in a galaxy, was caused by gas, heated to millions of degrees Celsius, from the destroyed star being swallowed by the black hole. The energy liberated in the process was equivalent to a supernova.
"Now, with all the data in hand, we have the smoking gun proof that this spectacular event has occurred," said coauthor Guenther Hasinger, also of MPE.
The black hole in the center of RXJ1242-11 is estimated to have a mass of about 100 million times Earth's sun. By contrast, the destroyed star probably had a mass about equal to the sun, making it a lopsided battle of gravity. "This is the ultimate David versus Goliath battle, but here David loses," said Hasinger.
The astronomers estimated about one percent of the star's mass was ultimately consumed, or accreted, by the black hole. This small amount is consistent with predictions the momentum and energy of the accretion process will cause most of the destroyed star's gas to be flung away from the black hole.
The force that disrupted the star in RXJ1242-11 is an extreme example of the tidal force caused by differences in gravity acting on the front and back of an object. The tidal force from the moon causes tides in Earth's oceans. A tidal force from Jupiter pulled Comet Shoemaker-Levy apart, before it plunged into the giant planet.
The odds stellar tidal disruption will happen in a typical galaxy are low, about one in 10,000 annually. If it happened at the center of the Milky Way Galaxy, 25,000 light-years from Earth, the resulting X-ray outburst would be about 50,000 times brighter than the brightest X-ray source in our galaxy, beside the sun, but it would not pose a threat to Earth.
Other dramatic flares have been seen from galaxies, but this is the first studied with the high-spatial resolution of Chandra and the high-spectral resolution of XMM-Newton. Both instruments made a critical advance. Chandra showed the RXJ1242-11 event occurred in the center of a galaxy, where the black hole lurks. The XMM-Newton spectrum revealed the fingerprints expected for the surroundings of a black hole, ruling out other possible astronomical explanations.Information and images about the event are available on the Internet at:
More information is available in ESO PR 26/03:
Miller presented these results today at a press conference at the meeting of the High Energy Astrophysics Division of the American Astronomical Society at Mt. Treblant, Quebec. His colleagues include Drs. Giuseppina Fabbiano of CfA, Cole Miller of the University of Maryland, and Andrew Fabian of the University of Cambridge.
"Evidence is mounting that these elusive intermediate-mass black holes may really exist," says Jon Miller. "The mystery, really, is how they can exist."
Black holes are objects so dense and with a gravitational potential so strong that nothing, not even light, can escape the pull if it ventures too close. Black holes are invisible, yet the gas and dust falling into a black hole are heated to high temperatures and glow furiously.
Scientists agree that there are at least two classes of black holes. Stellar black holes, with a mass of up to about ten suns, are the remains of massive stars whose cores have imploded. Supermassive black holes contain the mass of millions to billions of suns confined to a region about the size of our solar system. These monstrous objects likely form from immense gas clouds and are thought to reside in the cores of most galaxies.
Scientists are not in agreement over the existence of intermediate-mass black holes, however, which seem to harbor the mass of hundreds to tens of thousands of suns. Fabbiano first observed objects suspected to be intermediate-mass black holes in 1989 with the Einstein X-ray Observatory. Several more objects were discovered through the 1990s and were labeled ultra-luminous X-ray sources (ULXs), for they are exceedingly bright yet compact.
Over the last three years, several observations provided compelling evidence that ULXs were black holes. Yet scientists could not rule out the possibility that these bright objects were less exotic sources with all of their energy (or light) beamed in our direction, making them appear intrinsically brighter than they really are.
Jon Miller and his colleagues have new X-ray data that, when combined with recent optical and radio observations, strongly support the intermediate-mass black hole interpretation for two specific ULXs. The scientists observed these two objects in a spiral galaxy about 10 million light years from Earth called NGC 1313. One source, called NGC 1313 X-1, is approximately 3,000 light years from its galaxy's center. The other source, NGC 1313 X-2, is approximately 25,000 light years from the center. The XMM-Newton observations concentrated on the temperature of the gas orbiting the black holes in a disk, called an accretion disk.
The inner ring of the accretion disk, closest to the black hole, is the hottest part of the disk, glowing primarily in X-ray light. Perhaps counter-intuitive, however, is the black hole theory predicting that the inner ring of an accretion disk is hotter in small, stellar-mass black holes compared to supermassive black holes. This is because spacetime curves more gently near a large black hole than near a small one. Thus, the material falling into a supermassive black hole remains cooler over this larger surface area. The temperature of this inner disk is inversely proportional to the mass of the black hole, growing cooler with increasing black hole mass.
Jon Miller and his colleagues found the temperatures of NGC 1313 X-1 and X-2 to be in line with black holes containing at least 100 solar masses, and likely 200 to 500 solar masses. The scientists needed the superb resolution and collecting area afforded by XMM-Newton to be confident of the interpretation of their data.
While evidence supporting the existence of intermediate-mass black holes continues to flow in, scientists still do not know how such black holes would form. "Three basic scenarios have been suggested," says Cole Miller, "direct collisions and mergers of stars within globular clusters; the collapse of extremely massive stars that may have existed in the early Universe; or the merger of smaller black holes. Each scenario has strengths and limitations."
The images released include the black hole Cygnus X-1 and a gamma-ray burst. See the ESA press release:http://sci.esa.int/content/news/index.cfm?aid=21&cid=44&oid=31201
One of the most enigmatic stellar systems in our Milky Way Galaxy has been shown to harbour a very massive black hole. With 14 times more mass than the Sun , this is the heaviest known stellar black hole in the Galaxy.
Using the ISAAC instrument on the VLT 8.2-m ANTU telescope at the ESO Paranal Observatory, an international team of astronomers  peered into a remote area of the Milky Way to probe the binary system GRS 1915+105, located almost 40,000 light-years away.
They were able to identify the low-mass star that feeds the black hole by means of a steady flow of stellar material. A detailed follow-up study revealed how this star revolves around its hungry companion. The analysis of the orbital motion then made it possible to estimate the mass of the black hole.
The observation of the heavy black hole in GRS 1915+105 is opening up fundamental questions about how massive stellar black holes form, and whether or not such objects rotate around their own axes.
The Gemini Observatory press release on the deepest mid-infrared
image ever of the core and jet of M87 has been made public at:
The latest black hole list and diagram showing binary black holes, updated from Fig. 31-21, are kept by Jerry Orosz of the University of Utrecht at
See the simulations of Andrew Hamilton, University of Colorado at Berkeley, that show what it might be like to fall into a black hole and what wormholes are like at casa.colorado.edu/~ajsh/schw.shtml
Black holes are the stuff of science fiction. Or are they? Certainly one of the most compelling phenomena in the universe, black holes have inspired fantasies and nightmares alike. For years NASA's Hubble Space Telescope has been hard at work hunting for and learning about these awe-inspiring celestial voids. What are they? What do they look like? Is there one at the center of our Milky Way galaxy? Are they really "the point of no return"? Students can now find the answers to these and other questions in a fun and interactive way. In or out of the classroom, visit "No Escape: The Truth about Black Holes" on the Space Telescope Science Institute's "Amazing Space" Web site: