Archive for February 8th, 2012

February 8, 2012

How did some early black holes get so big so fast?

The supermassive black holes (SMBHs) found in the centers of large galaxies can be astonishingly large. The closest example to us is in the giant elliptical galaxy M87, and it’s estimated to be 6.6 billion solar masses (M). More distant examples can be even larger, more than 10 billion M (at distances ~300 million light-years).

Those are extremes. 1 or 2 billion M SMBHs are a little more common in our neighborhood, though still rare. Rather surprisingly, however, SMBHs that large can be found even in the very early universe. The largest yet discovered is about 2 billion M, and it’s 12.9 billion light-years away, at a redshift z=7.085. That SMBH reached its observed size only 765 million years after the big bang, i. e. perhaps 500 million years after the very first stars formed. It’s been a difficult problem to understand how SMBHs that large could have formed so quickly. A recently announced computer simulation of a large part of the very early universe may have come up with a good answer.

It is only barely possible to detect very bright objects (such as quasars or large galaxies) at redshifts z~7 with the best telescope technology today, and impossible to detect less bright objects (even the brightest stars) or objects at higher redshifts. So direct observation of the earliest stars – which may have begun to form as early as z~30, 100 million years after the big bang – is currently impossible, and computer simulations must be used to understand their properties and the process in which they formed.

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