Growing supermassive black holes from seeds

Astronomers announced Jan. 12, 2006 that they have found the first sample of intermediate-mass black holes in active galaxies – a discovery that will help in understanding the early universe.

“These are local analogues of the `seed’ black holes from which supermassive black holes formed,” said Jenny E. Greene of the Harvard-Smithsonian Center for Astrophysics (CfA). Greene presented these results with Luis C. Ho of Carnegie Observatories at the 207th meeting of the American Astronomical Society in Washington, D.C.

“Supermassive black holes (with masses of millions to billions of times the mass of the Sun) are found in the centers of most, if not all, massive galaxies, and the black hole masses scale with the galaxy masses, so that larger black holes reside in larger galaxies,” said Greene. “We want to understand how this connection is established, and more specifically, what role black holes play in the evolution of galaxies.”

Black holes probably evolve as material, such as gas, dust, stars and even other black holes, gets sucked in by the strong gravitational pull. “However, we cannot observe the starting conditions of the black holes directly,” said Ho. “How massive were they? How and when were they made? These are crucial questions to answer if we want to understand how black holes impact the growth of galaxies.”

The black hole “seeds” originally may have formed from the explosions of the first stars or from the collapse of clumps of gas in the early universe. Each of these different formation scenarios leads to very different numbers of intermediate-mass black holes left over in the universe today. Until now, few good candidates had been found.