12 February 2009

Speaker: Mitch Begelman (JILA)

Title:The First Supermassive Black Holes?

Abstract:The existence of a supermassive black hole in nearly every galactic nucleus is no longer in doubt, but the question of how these black holes formed is wide open. I will argue that they could have formed directly via the accumulation and collapse of gigantic starlike objects, if the infall rate of gas into the nucleus was high enough. Black hole formation by very rapid infall could have occurred in pregalactic haloes as early as redshifts ~10-20, at lower redshifts in the nuclei of protogalaxies, or even as late as the quasar era in fairly mature galaxies. Global gravitational instabilities get rid of excess angular momentum and the infalling gas forms a self-gravitating, optically thick structure. As matter piles on, the core burns through its nuclear fuel and eventually collapses to form a black hole with a mass of between 10^4 and >10^6 solar masses. The black hole can then grow further by accreting from its envelope at an extremely super-Eddington rate, possibly increasing in mass by another order of magnitude before expelling the envelope. "Quasistars" - shrouded black holes accreting from massive envelopes - should resemble ultraluminous red giants and might be detectable with the James Webb Space Telescope.

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