Astronomer Finds Evidence Of Binary Black Holes

June 18, 1996

Astronomer Finds Evidence of Binary Black Holes
For Immediate Release

Contact: Robert Sheldon
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Lincoln (Neb.) June 18, 1996 - It's hard enough to visualize even one black hole - a region of space where gravity is so powerful that nothing, not even light, can escape its massive attraction. Even harder to contemplate is the idea that some galaxies are blessed with two giant black holes revolving around each other.

Martin Gaskell, professor of physics and astronomy at the University of Nebraska-Lincoln, believes there are binary black holes orbiting one another in the centers of many galaxies. He was led to this conclusion by the study of the motions of gas in quasars.

"We think of black holes as something where things fall in and canUt escape," Gaskell said. "If so, how does light get out?"

Quasars, or "quasi-stellar radio sources," are intense sources of energy in the centers of galaxies. The light they emit can be so strong that at great distances the glare of the quasar drowns out the light of the surrounding galaxy. Gaskell said that about 90 percent of astronomers believe that quasars are powered by giant black holes and that black holes are many times better at converting matter into energy than hydrogen bombs. In quasars, some of the matter is apparently converted into energy and escapes as light before it can fall into the black hole.

In 1983, Gaskell drew attention to a class of quasars in which the gas was moving at thousands of miles per second with respect to the galaxies where they are located. He proposed that the differences in apparent speed were due to the gas clouds being associated with two black holes orbiting each other.

Gaskell said many astronomers also believe that many giant black holes exist at the centers of many or most of the millions of known galaxies. Recent research by Gaskell provides evidence that pairs of giant black holes do indeed exist and probably formed when their galaxies collided.

He reasoned that over a decade or so it should be possible to see changes in the apparent velocities of the gas as the two black holes moved in their orbits round each other. In a paper published in the June 20 issue of the Astrophysical Journal Letters, Gaskell reported the discovery of just such changes in the apparent speed of assemblages of gas in a particular quasar, 3C 390.3. His research used data gathered over more than two decades.

"The exciting thing my measurements show is that there is a clear unmistakable trend in the velocity of the gases over time," Gaskell said. "My interpretation of the change in apparent velocity of the gases in 3C 390.3 is that it is due to two black holes orbiting around each other."

Gaskell's calculations show that the two black holes in 3C 390.3 have a combined mass about 4 billion times the mass of the sun. Gravitational radiation will eventually cause the black holes to spiral together and merge into one large black hole.

Unfortunately, two orbiting giant black holes may take centuries to go around each other, so it might take observations far into the future before final proof of what Gaskell's measurements indicate can be firmly established.
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University of Nebraska-Lincoln

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