184 research outputs found
The Formation of Population III Binaries from Cosmological Initial Conditions
Previous high resolution cosmological simulations predict the first stars to
appear in the early universe to be very massive and to form in isolation. Here
we discuss a cosmological simulation in which the central 50 solar mass clump
breaks up into two cores, having a mass ratio of two to one, with one fragment
collapsing to densities of 10^{-8} g/cc. The second fragment, at a distance of
800 astronomical units, is also optically thick to its own cooling radiation
from molecular hydrogen lines, but is still able to cool via collision-induced
emission. The two dense peaks will continue to accrete from the surrounding
cold gas reservoir over a period of 10^5 years and will likely form a binary
star system.Comment: Accepted by Science, first published online on July 9, 2009 in
Science Express. 16 pages, 4 figures, includes supporting online materia
Protostellar Feedback Processes and the Mass of the First Stars
We review theoretical models of Population III.1 star formation, focusing on
the protostellar feedback processes that are expected to terminate accretion
and thus set the mass of these stars. We discuss how dark matter annihilation
may modify this standard feedback scenario. Then, under the assumption that
dark matter annihilation is unimportant, we predict the mass of stars forming
in 12 cosmological minihalos produced in independent numerical simulations.
This allows us to make a simple estimate of the Pop III.1 initial mass function
and how it may evolve with redshift.Comment: 6 pages, Proceedings of 'The First Stars and Galaxies: Challenges for
the Next Decade", Austin, TX, March 8-11, 201
Photoionization of Clustered Halos by the First Stars
We present numerical simulations of the photoevaporation of cosmological
halos clustered around a 120 M primordial star, confining our study to
structures capable of hosting Population III star formation. The calculations
include self-consistent multifrequency conservative transfer of UV photons
together with nine-species primordial chemistry and all relevant radiative
processes. The ultimate fates of these halos varies with central density and
proximity to the central source but generally fall into one of four categories.
Diffuse halos with central densities below 2 - 3 cm are completely
ionized and evaporated by the central star anywhere in the cluster. More
evolved halo cores at densities above 2000 cm are impervious to both
ionizing and Lyman-Werner flux at most distances from the star and collapse of
their cores proceeds without delay. Radiative feedback in halos of intermediate
density can be either positive or negative, depending on how the I-front
remnant shock both compresses and deforms the core and enriches it with H.
We find that the 120 M star photodissociates H in most halos within
the cluster but that catalysis by H- rapidly restores molecular hydrogen within
a few hundred Kyr after the death of the star, with little delay in star
formation. Our models exhibit significant departures from previous
one-dimensional spherically-symmetric simulations, which are prone to serious
errors due to unphysical geometric focusing effects.Comment: 5 pages, 5 figures, to appear in "First Stars III", eds. B. O'Shea,
A. Heger and T. Abe
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