For release: 02/18/04
Release #: 04-021
For the first time, thanks to telescopes including NASA's Chandra X-ray Observatory, astronomers have witnessed a supermassive black hole ripping apart a star and consuming a portion of it. The event has long been predicted by theory, but has never before been observed. The Marshall Center manages the Chandra program.Photo: Illustration of a black hole destroying a star in the galaxy RXJ1242-11 (Illustration: NASA/CXC/M. Weiss; X-ray: NASA/CXC/MPE/S. Komossa et al.; Optical: ESO/MPE/S. Komossa)
For the first time, thanks to two orbiting X-ray observatories, astronomers have witnessed 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, has long been predicted by theory, but has never before been observed.
Astronomers believe that a doomed star came too close to a giant black hole after a close encounter with another star threw it off course. 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 the 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, who led the international team of researchers. "This unlucky star just wandered into the wrong neighborhood."
While other observations have hinted that 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 (ROSAT), 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 from the destroyed star that was heated to millions of degrees Celsius before being swallowed by the black hole. The energy liberated in this process is equivalent to that of a supernova. "Now, with all of 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 RX J1242-11 is estimated to have a mass about 100 million times the Sun. By contrast, the destroyed star probably had a mass about equal to that of 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 that about one percent of the mass of the star was ultimately consumed, or accreted, by the black hole. This small amount is consistent with predictions that 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, and tidal force from Jupiter pulled Comet Shoemaker-Levy apart before it plunged into the giant planet.
The odds that stellar tidal disruption will happen in a typical galaxy are low, about one in ten thousand per year. If it happened at the center of the Milky Way Galaxy some 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, but would not pose a threat to Earth.
Other dramatic flares have been seen from galaxies, but this is the first to have been studied with the high-spatial resolution of Chandra and the high-spectral resolution of XMM-Newton. Both instruments made a critical advance. Chandra showed that the RXJ 1242-11 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.
NASA's Marshall Space Flight Center , Huntsville , Ala. , manages the Chandra program for the Office of Space Science, NASA Headquarters, 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:
Guido De Marchi
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