Copyright by Athena Ranice Stacy 2011 - The University of Texas at ...

which fragmented due to gravitational instability. Similar to the sink mergers
seen in our calculation, in their simulation the secondary stars that formed in
the disk collided with the most massive star. By the end of their simulation,
which was halted after ∼ 60,000 yr, the system had evolved into a binary
with stars of mass ∼ 30 and 40 M⊙, masses fairly close to those of the two
largest sinks in our simulation. Their calculation, however, included dust
opacity as well as radiation pressure from the stars, and their initial conditions
were typical of present-day star formation. Their accretion and fragmentation
timescales were also much longer than those found in our calculation, but the
overall qualitative results were alike.
Thus, the formation of binary and multiple systems within disk struc-
tures is likely not limited to modern-day star formation and can be found even
in the primordial case, arising from cosmological initial conditions. Binary
and multiple systems may be much more common in the Pop III case than
previously thought. As similarly argued in Clark et al. (2008), this is because
most cosmological simulations do not follow the gas evolution for many years
after the first protostar has formed, and fragmentation may not typically occur
until after the simulations are stopped. For instance, the second protostar in
our calculation did not form until 300 yr after the first, while the calculation
of Turk et al. (2009) was stopped only 200 yr after the first protostar formed.
If Pop III binaries and multiples are actually common, then this has im-
portant implications for the final fate and observational signature of Pop III.1
stars, those zero-metallicity stars that have not yet been influenced by any pre-
vious stellar generation (e.g. Bromm et al. 2009). The presence of multiple
accretors in our simulation did not seem to affect the accretion rate onto the
largest sink as compared to previous work (Bromm & Loeb 2004). However,
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