Disk fragmentation and intermittent accretion onto supermassive stars
  Supermassive stars (SMSs) with $\sim10^{4-5}~\mathrm{M}_{\odot}$ are
candidate objects for the origin of supermassive black holes observed at
redshift $z$>6. They are supposed to form in primordial-gas clouds that provide
the central stars with gas at a high accretion rate, but their growth may be
terminated in the middle due to the stellar ionizing radiation if the accretion
is intermittent and its quiescent periods are longer than the Kelvin-Helmholtz
(KH) timescales at the stellar surfaces. In this paper, we examine the role of
the ionizing radiation feedback based on the accretion history in two possible
SMS-forming clouds extracted from cosmological simulations, following their
evolution with vertically-integrated two-dimensional hydrodynamic simulations
with detailed thermal and chemical models. The consistent treatment of the gas
thermal evolution is crucial for obtaining the realistic accretion history, as
we demonstrate by performing an additional run with a barotropic equation of
state, in which the fluctuation of the accretion rate is artificially
suppressed. We find that although the accretion becomes intermittent due to the
formation of spiral arms and clumps in gravitationally unstable disks, the
quiescent periods are always shorter than the KH timescales, implying that SMSs
can form without affected by the ionizing radiation.
