The Burst Mode of Accretion in Primordial Protostars
  We study the formation and long-term evolution of primordial protostellar
disks harbored by first stars using numerical hydrodynamics simulations in the
thin-disk limit. The initial conditions are specified by pre-stellar cores with
distinct mass, angular momentum, and temperature. This allows us to probe
several tens of thousand years of the disk's initial evolution, during which we
observe multiple episodes of fragmentation leading to the formation of
gravitationally bound gaseous clumps within spiral arms. These fragments are
torqued inward due to gravitational interaction with the spiral arms on
timescales of 10^3 - 10^4 yr and accreted onto the growing protostar, giving
rise to accretion and luminosity bursts. The burst phenomenon is fueled by
continuing accretion of material falling onto the disk from the collapsing
parent core, which replenishes the mass lost by the disk due to accretion, and
triggers repetitive episodes of disk fragmentation. We show that the burst
phenomenon is expected to occur for a wide spectrum of initial conditions in
primordial pre-stellar cores and speculate on how the intense luminosities
(~10^7 solar luminosities) produced by this mechanism may have important
consequences for the disk evolution and subsequent growth of the protostar.
