Samplings: November 2009

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Computer simulation shows radiation (white) produced by a black hole in the early universe, and its effect on nearby gas (blue)

KIPAC/Stanford/SLAC M. Alvaraz, T. Abel, and J. Wise

Black holes are gluttons, sucking in everything nearby with their immense gravitational fields. In the early stages of the universe, however, black holes had slim pickings on which to feed, a new study suggests. What’s more, they had only themselves to blame.

Not everyone realizes that black holes emit copious radiation. The rays don’t come from the holes themselves, of course, but from the heated and compressed matter hurtling toward them. The radiation heats other nearby ordinary matter, which typically falls into the black hole like all the rest. But in the early universe, say Marcelo A. Alvarez and two colleagues at Stanford University, the halos of dark matter that surround black holes were quite skimpy compared with the halos around modern black holes. The holes and their halos weren’t sufficiently massive to gravitationally entrap the extra radiation-heated matter, and it simply diffused away, depriving the beasts of further fodder. The three astrophysicists ran a computer simulation of that effect and found that as a result, early black holes grew much more slowly than previously thought—by less than 1 percent during their first 200 million years.

But today some black holes are huge; how did they get so big? One possibility, Alvarez’s team says, is that dozens of the early black holes eventually came together in clusters. In each one, radiation from the holes may have enabled enormous gas clouds to build up, then collapse under their own weight to form a giant black hole. (Astrophysical Journal)