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

which has already detected GRBs at a redshift as high as z ≈ 8.2 (Salvaterra
et al. 2009; Tanvir et al. 2009), and may also be detected by possible future
missions such as JANUS and EXIST.
We emphasize the caveat that we did not fully resolve stellar scales.
We have measured the total angular momentum accreted within racc 50 AU
of the star, and we have argued that a Keplerian disk and perhaps a binary is
expected to form on sub-sink scales, still leaving enough angular momentum
for one or two rapidly rotating stars. However, there are further processes
which can transport angular momentum away from rotating stars. For in-
stance, angular momentum may be lost through stellar winds, but the mass
and angular momentum loss through winds is expected to be much lower for
low-metallicity and Pop III stars than for higher-metallicity stars (Nugis and
Lamers 2000; Kudritzki 2002). Other processes include disk torques induced
by gravitational instability as well as viscous torques, which have a variety of
sources including hydromagnetic instability (see, e.g. Papaloizou and Lin 1995
for a review).
In particular, the magneto-hydrodynamic (MHD) aspect of Pop III star
formation is still very uncertain (e.g. Maki and Susa 2007), and we therefore
here neglect any angular momentum loss due to magnetic torques. Earlier
work, however, gives some hint as to the possible effect of magnetic fields.
Machida et al. (2008) conclude that if a star-forming primordial cloud has a
large enough initial magnetic field (B > 10 −9 [n/10 3 cm −3 ] 2/3 G), a protostellar
jet will be driven provided that the cloud’s rotational energy is less than its
magnetic energy. However, Xu et al. (2008) find that the Biermann battery
mechanism and flux freezing alone will not amplify magnetic fields in a collaps-
ing halo quickly enough to reach this threshold value. In contrast, small-scale
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