Formation and Coalescence of Cosmological Supermassive Black Hole Binaries in Supermassive Star Collapse
August 19, 2013
Abstract: The overwhelming observational evidence for supermassive black holes in the early Universe at high redshifts z>7 produces a serious problem: how could these black holes have formed? The two most promising pathways (hierarchical galaxy mergers and accretion onto collapsed Population III stars) have been ruled out by a number of recent studies. A possible alternative pathway for supermassive black hole formation at high redshifts is the collapse of a supermassive star that may have formed in the direct collapse of a primordial gas cloud. We self-consistently simulate the collapse of rapidly rotating supermassive stars from the onset of collapse using three-dimensional general-relativistic hydrodynamics with fully dynamical spacetime evolution. We show that seed perturbations in the progenitor can lead to the formation of a system of two high-spin supermassive black holes, which inspiral and merge under the emission of powerful gravitational radiation. The gravitational-wave signals could be observed at redshifts z>10 with the DECIGO or Big Bang Observer gravitational-wave observatories, assuming supermassive stars in the mass range 10^4-10^6 M_ odot. The potential detection of such signals may inform cosmology about the formation process of supermassive black holes at high redshifts.