The importance of magnetic fields for the initial mass function of the
  first stars
  Magnetic fields play an important role for the formation of stars in both
local and high-redshift galaxies. Recent studies of dynamo amplification in the
first dark matter haloes suggest that significant magnetic fields were likely
present during the formation of the first stars in the Universe at redshifts of
15 and above. In this work, we study how these magnetic fields potentially
impact the initial mass function (IMF) of the first stars. We perform 200
high-resolution, three-dimensional (3D), magneto-hydrodynamic (MHD) simulations
of the collapse of primordial clouds with different initial turbulent magnetic
field strengths as predicted from turbulent dynamo theory in the early
Universe, forming more than 1100 first stars in total. We detect a strong
statistical signature of suppressed fragmentation in the presence of strong
magnetic fields, leading to a dramatic reduction in the number of first stars
with masses low enough that they might be expected to survive to the present
day. Additionally, strong fields shift the transition point where stars go from
being mostly single to mostly multiple to higher masses. However, irrespective
of the field strength, individual simulations are highly chaotic, show
different levels of fragmentation and clustering, and the outcome depends on
the exact realisation of the turbulence in the primordial clouds. While these
are still idealised simulations that do not start from cosmological initial
conditions, our work shows that magnetic fields play a key role for the
primordial IMF, potentially even more so than for the present-day IMF.
