Donald Savage
Headquarters, Washington                  November 19, 2002
(Phone: 202/358-1727)

Steve Roy
Marshall Space Flight Center, Huntsville, Ala.
(Phone: 256/544-6535)

Megan Watzke
Chandra X-ray Observatory Center, Cambridge, Mass.
(Phone: 617/496-7998)

RELEASE: 02-222

NEVER BEFORE SEEN: TWO SUPERMASSIVE BLACK HOLES IN SAME 
GALAXY

     For the first time, scientists have proof two 
supermassive black holes exist together in the same galaxy, 
thanks to data from NASA's Chandra X-ray Observatory. These 
black holes are orbiting each other and will merge several 
hundred million years from now, to create an even larger 
black hole resulting in a catastrophic event that will 
unleash intense radiation and gravitational waves.

The Chandra image reveals that the nucleus of an 
extraordinarily bright galaxy, known as NGC 6240, contains 
not one, but two giant black holes, actively accreting 
material from their surroundings. This discovery shows that 
massive black holes can grow through mergers in the centers 
of galaxies, and that these enigmatic events will be 
detectable with future space-borne gravitational wave 
observatories.

"The breakthrough came with Chandra's ability to clearly 
distinguish the two nuclei, and measure the details of the X-
radiation from each nucleus," said Guenther Hasinger, of the 
Max Planck Institute for Extraterrestrial Physics in Germany, 
a coauthor of an upcoming Astrophysical Journal Letters paper 
describing the research. "These cosmic fingerprints revealed 
features characteristic of supermassive black holes -- an 
excess of high-energy photons from gas swirling around a 
black hole, and X-rays from fluorescing iron atoms in gas 
near black holes," he said.

Previous X-ray observatories had shown that the central 
region produces X-rays, while radio, infrared and optical 
observations had detected two bright nuclei, but the nature 
of this region remained a mystery. Astronomers did not know 
the location of the X-ray source, or the nature of the two 
bright nuclei.

"With Chandra, we hoped to determine which one, if either, of 
the nuclei was an active supermassive black hole," said 
Stefanie Komossa, also of the Max Planck Institute, lead 
author of the paper on NGC 6240. "Much to our surprise, we 
found that both were active black holes!"

At a distance of about 400 million light-years, NGC 6240 is a 
prime example of a massive galaxy in which stars are forming 
at an exceptionally rapid rate due to a recent collision and 
subsequent merger of two smaller galaxies. Because of the 
large amount of dust and gas in such galaxies, it is 
difficult to peer deep into their central regions with 
optical telescopes. However, X-rays emanating from the 
galactic core can penetrate the veil of gas and dust.

"The detection of a binary black hole supports the idea that 
black holes can grow to enormous masses in the centers of 
galaxies by merging with other black holes," said Komossa. 
"This is important for understanding how galaxies form and 
evolve," she said.

Over the course of the next few hundred million years, the 
two black holes in NGC 6240, which are about 3000 light-years 
apart, will drift toward one another and merge to form an 
even larger supermassive black hole. Toward the end of this 
process an enormous burst of gravitational waves will be 
produced several hundred million years from now.

These gravitational waves will spread through the universe 
and produce ripples in the fabric of space, which would 
appear as minute changes in the distance between any two 
points. NASA's planned space-based detector, LISA (Laser 
Interferometer Space Antenna), will search for gravitational 
waves from massive black-hole mergers. These events are 
estimated to occur several times each year in the observable 
universe.

"This is the first time we see a binary black hole in action, 
the smoking gun for something that will become a major 
gravitational wave burst in the future," said Hasinger.

Chandra observed NGC 6240 for 10.3 hours with the Advanced 
CCD Imaging Spectrometer (ACIS). Other members of the team 
are Vadim Burwitz and Peter Predehl of the Max Planck 
Institute, Jelle Kaastra of the Space Research Organization 
Netherlands and Yasushi Ikebe of the University of Maryland 
in Baltimore.

NASA's Marshall Space Flight Center in Huntsville, Ala., 
manages the Chandra program for the Office of Space Science, 
Washington, and TRW, Inc., Redondo Beach, Calif., is the 
prime contractor for the spacecraft. The Smithsonian's 
Chandra X-ray Center controls science and flight operations 
from Cambridge, Mass.

Images and additional information about this result are 
available at:
http://chandra.harvard.edu
and
http://chandra.nasa.gov

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