Formation of an embryonic supermassive star in the first galaxy
  We studied the gravitational collapse of a warm (~8000 K) primordial-gas
cloud as a candidate progenitor for a supermassive star (SMS; >10^5 Msun) using
a three-dimensional hydrodynamical simulation, including all the relevant
cooling processes of both H_2 and H, which can potentially induce cloud
fragmentation. This is the first simulation of this kind to resolve protostar
formation. We find that the cloud undergoes runaway collapse without a major
episode of fragmentation. Although the H_2 fraction jumps by a large factor via
the three-body reaction at ~10^-13 g/cm^3, its cooling remains inefficient due
to the optical thickness, and the temperature remains >3000 K. When the central
core of the cloud becomes opaque to continuum radiation at ~10^-8 g/cm^3, a
hydrostatic protostar with ~0.2 Msun is formed. The protostar grows to the mass
~1 Msun and the radius ~2 AU within ~1 yr via rapid accretion of dense
filamentary flows. With high accretion rate ~2 Msun/yr, the protostar is
expected to turn into a SMS within its lifetime, eventually collapsing to a
seed for the supermassive black hole observed in the early Universe at z~7.
