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Black Hole Bonanza: Scientists Answer Cosmic Riddle
By Maia Weinstock
Staff Writer
posted: 02:54 pm ET
27 March 2000
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black_hole_eats_000327 If youve been struggling to keep up with your New Years diet, dont feel so bad. It now seems the biggest binge-eaters of all arent even human theyre black holes. In related studies, British and American astronomers recently found compelling evidence for a growing theory of how black holes evolve: by eating everything in sight, including stars, dust and gas. The discovery is helping researchers further understand the relationship between black holes and galaxies. Black holes are believed to reside at the center of most galaxies. Yet for years, astronomers have struggled with a sort of galactic chicken-egg dilemma: Did massive black holes exist before their galaxies formed around them? Or did they grow over time by taking in mass from a previously existing galaxy? Now, the answer is starting to literally shine through. By comparing the brightness and age of a number of nearby galaxies, three British scientists determined that young black holes actually have less mass than their older counterparts. This remarkable result implies that black holes start out small, then gradually build up their masses by consuming matter throughout their lifetime. "This is the first direct evidence that black holes grow over time, and it gives us the first clue to how black holes form," said Michael Merrifield, an astronomer at the University of Nottingham. "The discovery implies that [black holes] cannot be entirely primordial, predating the galaxies that contain them." Merrifield and his colleagues Duncan Forbes and Alejandro Terlevich, both of the University of Birmingham, analyzed data on galaxies that are known to contain black holes at their centers. The galaxies included the familiar Andromeda galaxy, which lies some 2.5 million light-years away from Earth. "I honestly didnt believe that our measurements of either black hole mass or galaxy age would be good enough to allow us to detect the [size/age] correlation," said Merrifield. "I was pleasantly surprised to discover that they are!" Pictorial proof As if the British astronomers accomplishments werent exciting enough, a team of scientists at Ohio State University recently provided close-up images of dust masses swirling into the center of several galaxies. The American scientists say that this dust is likely the "food" that the galaxies central black holes gobble up to gain weight. 
Markanian 573 as seen by Hubble in black and white (left) and infrared (right) Ohio State astronomers Richard Pogge and Paul Martini used NASAs Hubble Space Telescope to shoot images of nearby galaxies with two different cameras: one that records visible light and one that records infrared. The combination of visible and infrared images revealed an amazing view of the galaxies hearts. Whats more, according to Duncan Forbes, the resulting images back up the British scientists work. "The Ohio astronomers have provided evidence of the fuel for black holes: gas and dust," he said. "We have shown that [something] is actually working, feeding a steady supply of material into black holes," noted Merrifield. "The team at Ohio State has found a mechanism by which material might be funneled down toward a black hole via small-scale spiral features. The two results are complementary." Scientists hope to continue learning how black hole formation is linked to the evolution of galaxies and stars. Researchers say that if a black hole lies at the center of our own Milky Way galaxy, it seems not to be too hungry at the moment. "All the present data suggests we have a 3 million-solar-mass black hole in the Milky Way," said Pogge in a statement released by Ohio State University. "But its about as quiescent as they get."
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