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