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Two Supermassive Black Holes in Same Galaxy

Analyzing new data, scientists have proof of that a pair of 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 (Fig. 1). 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 Günther Hasinger, of the Max-Planck-Institute for extraterrestrial Physics in Germany, and a coauthor of the Astrophysical Journal Letters paper describing the research. "These cosmic fingerprints revealed features that are characteristic of supermassive black holes: an excess of high energy photons from gas swirling around a black hole (Fig. 2), and X-rays from fluorescing iron atoms in gas near the black hole" (Fig. 3).

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, and 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 (see movie 2). 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."

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 (movie 3).

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. The merging of two supermassive Black Holes like those in NGC 6240 will create the most powerful gravitational waves in the universe. LISA (Laser Interferometer Space Antenna), the space-based detector planned by NASA and ESA, 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 that we see a binary black hole in action, the smoking gun for something which 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-Institut für extraterrestrische Physik, 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. The German Contribution to Chandra was funded by the Deutsches Zentrum für Luft- und Raumfahrt (DLR).

 

Image credit: MPE (optical image provided by Bill Keel)
click on image to get a 0.6 Mb TIFF version

Figure 1: X-ray view of the "heart" of the ultraluminous galaxy NGC 6240: detection of a binary black hole.
left is the view of NGC 6240 as seen with a telescope from Earth. The arcs and "arms" are the result of the collision of two galaxies in the past which now are in the process of merging. Hidden by massive dust and gass, the central part of the galaxy is not visible in the optical wavelength band. X-rays, beeing much more penetrating, alow to view the center of the galaxy. The Chandra X-ray image shown at right led to the detection of two super massive black holes which reveal themselves by the very high energy X-ray emission which originates in their immediate vicinity (black circles). The X-ray image is color coded: red marks low energy X-ray emission, blue marks high energy X-ray emission. See also movie 1.

 

Image credit: NASA/MPE
Figure 2: The X-ray emission (blue) which identifies the binary black hole is combined here with a Hubble Space Telescope (HST) image (yellow) of the central region of NGC 6240.

 

Image credit: NASA/MPE
Figure 3: Besides the high energy X-ray emission concentrated in the nuclear region, there is also extended low energy X-ray emission (red) which is shown here as an overlay on a HST image (yellow and blue). This low energy X-ray emission is not connected to the two central black holes, but is the afterglow of a starburst that occured long ago in the center of NGC 6240. In the past, there was a burst of supernova exposions in the central region which ejected their outer shells into the interstellar space. Once these stellar winds hit the interstellar medium they heat up and glow in X-rays.

 

Image credit: CXC/M. Weiss
Figure 4: An artist's conception shows a black hole surrounded by a disk of hot gas, and a large doughnut or torus of cooler gas and dust. The light blue shimmer on the back of the torus is due to fluorescence of iron atoms excited by X-rays from the hot gas disk.

  Three animations in Quicktime (.mov) format :


More images, additional information and press articles about this result are available at:
( indicates an external link!)

Original paper in Astrophysical Journal Letters 582, L15-L19, 2003.

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Space Today ,  Astronomy.com ,  BBC ,
Christian Science Monitor ,  New York Times ,  United Press International ,
Washington Post ,  Space.com ,  Netzeitung.de ,  Astronomy Picture of the Day.


Contact Information:

Prof. Dr. Günther Hasinger
Max-Planck-Institut für extraterrestrische Physik
Giessenbachstraße
85748 Garching
Phone: +49-89-30000-3402
Fax: +49-89-30000-3569
E-Mail: ghasinger@mpe.mpg.de

Dr. Stefanie Komossa
Max-Planck-Institut für extraterrestrische Physik
Giessenbachstraße
85748 Garching
Phone: +49-89-30000-3577
Fax: +49-89-30000-3569
E-Mail: skomossa@mpe.mpg.de

© Max-Planck-Institut für extraterrestrische Physik

Impressum
last update: 2002-12-18
editor: Helmut Steinle   (email: hcs@mpe.mpg.de)