Giant Black Hole Rips Apart Unlucky
Star In Cosmic Reality Show
The accompanying illustration depicts how such an event may have occurred. A
close encounter with another star put the doomed star (orange circle) on a path
that took it near a supermassive black hole. The enormous gravity of the giant
black hole stretched the star until it was torn apart. Because of the momentum
and energy of the accretion process, only a few percent of the disrupted star's
mass (indicated by the white stream) was swallowed by the black hole, while the
rest of was flung away into the surrounding galaxy. (Credit: Illustration:
NASA/CXC/M.Weiss; X-ray: NASA/CXC/MPE/S.Komossa et al.; Optical:
ESO/MPE/S.Komossa)
ScienceDaily (Feb. 19, 2004) — 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.