Formation and Coalescence of Cosmological Supermassive Black Hole Binaries in Supermassive Star Collapse

TL;DR

This study simulates the collapse of rapidly rotating supermassive stars, revealing the formation, inspiral, and merger of supermassive black hole binaries with significant gravitational wave emissions detectable at high redshifts.

Contribution

It provides the first self-consistent 3D general-relativistic simulation of supermassive star collapse leading to binary black hole formation and gravitational wave prediction.

Findings

Formation of high-spin supermassive black hole binaries.

Black hole mergers produce detectable gravitational waves at z>10.

Remnant black hole has a spin parameter a^*=0.9.

Abstract

We study the collapse of rapidly rotating supermassive stars that may have formed in the early Universe. By self-consistently simulating the dynamics 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 that 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 Msol. The remnant is rapidly spinning with dimensionless spin a^*=0.9. The surrounding accretion disk contains ~10% of the initial mass.