  One possible scenario for the formation of massive black holes (BHs) in the
early Universe is from the direct collapse of primordial gas in atomic-cooling
dark matter haloes in which the gas is unable to cool efficiently via molecular
transitions. We study the formation of such BHs, as well as the accretion of
gas onto these objects and the high energy radiation emitted in the accretion
process, by carrying out cosmological radiation hydrodynamics simulations. In
the absence of radiative feedback, we find an upper limit to the accretion rate
onto the central object which forms from the initial collapse of hot (~ 10^4 K)
gas of the order of 0.1 MSun per year. This is high enough for the formation of
a supermassive star, the immediate precursor of a BH, with a mass of the order
of 10^5 MSun. Assuming that a fraction of this mass goes into a BH, we track
the subsequent accretion of gas onto the BH self-consistently with the high
energy radiation emitted from the accretion disk. Using a ray-tracing algorithm
to follow the propagation of ionizing radiation, we model in detail the
evolution of the photoionized region which forms around the accreting BH. We
find that BHs with masses of the order of 10^4 MSun initially accrete at close
to the Eddington limit, but that the accretion rate drops to of order 1 percent
of the Eddington limit after ~ 10^6 yr, due to the expansion of the gas near
the BH in response to strong photoheating and radiation pressure. One signature
of the accretion of gas onto BHs formed by direct collapse, as opposed to
massive Pop III star formation, is an extremely high ratio of the luminosity
emitted in He II 1640 to that emitted in H_alpha (or Ly_alpha); this could be
detected by the James Webb Space Telescope. Finally, we briefly discuss
implications for the coevolution of BHs and their host galaxies.
