  There is compelling evidence that supermassive black holes (SMBHs) exist. Yet
the origin of these objects, or their seeds, is still unknown. We are
performing general relativistic simulations of gravitational collapse to black
holes in different scenarios to help reveal how SMBH seeds might arise in the
universe. SMBHs with ~ 10^9 solar masses must have formed by z > 6, or within
10^9 yrs after the Big Bang, to power quasars. It may be difficult for gas
accretion to build up such a SMBH by this time unless the initial seed black
hole already has a substantial mass. One plausible progenitor of a massive seed
black hole is a supermassive star (SMS). We have followed the collapse of a SMS
to a SMBH by means of 3D hydrodynamic simulations in post-Newtonian gravity and
axisymmetric simulations in full general relativity. The initial SMS of
arbitrary mass M in these simulations rotates uniformly at the mass--shedding
limit and is marginally unstable to radial collapse. The final black hole mass
and spin are determined to be M_h/M ~ 0.9 and J_h/M_h^2 ~ 0.75. The remaining
mass goes into a disk of mass M_{disk}/M ~ 0.1. This disk arises even though
the total spin of the progenitor star, J/M^2 = 0.97, is safely below the Kerr
limit. The collapse generates a mild burst of gravitational radiation.
Nonaxisymmetric bars or one-armed spirals may arise during the quasi-stationary
evolution of a SMS, during its collapse, or in the ambient disk about the hole,
and are potential sources of quasi-periodic waves, detectable by LISA.
