3,849 research outputs found
Pop III Stellar Masses and IMF
We provide a status report on our current understanding of the mass scales
for Pop III.1 and Pop III.2 stars. Since the last review (Norman 2008),
substantial progress has been made both numerically and analytically on the
late stages of protostellar cloud core collapse, protostar formation and
accretion, and stellar evolution taking into account cloud core properties and
radiative feedback effects. Based on this, there are growing indications that
primordial stars forming from purely cosmological initial conditions (Pop
III.1) were substantially more massive than stars forming in preionized gas
(Pop III.2) where HD cooling is important. Different stellar endpoints are
predicted for these two types of Pop III stars with different chemical
enrichment signatures: the former die as pair instability supernovae or
intermediate mass black holes, whereas the latter die as iron core-collapse
supernovae, leaving behind neutron star and stellar black hole remnants. We
review recent simulations which show evidence for binary fragmentation at high
densities, and comment on the significance of these results. We then summarize
an attempt to directly calculate the Pop III.1 IMF taking into account the
latest numerical and analytical models. We conclude with suggestions for the
kind of simulations needed next to continue improving our understanding of Pop
III star formation, which is a necessary input to understanding high redshift
galaxy formation.Comment: 11 pages, 3 figures, Proceedings of "The First Stars and Galaxies:
Challenges for the Next Decade", Austin, TX, March 8-11, 201
Ionization Front Instabilities in Primordial H II Regions
Radiative cooling by metals in shocked gas mediates the formation of
ionization front instabilities in the galaxy today that are responsible for a
variety of phenomena in the interstellar medium, from the morphologies of
nebulae to triggered star formation in molecular clouds. An important question
in early reionization and chemical enrichment of the intergalactic medium is
whether such instabilities arose in the H II regions of the first stars and
primeval galaxies, which were devoid of metals. We present three-dimensional
numerical simulations that reveal both shadow and thin-shell instabilities
readily formed in primordial gas. We find that the hard UV spectra of
Population III stars broadened primordial ionization fronts, causing H2
formation capable of inciting violent thin- shell instabilities in D-type
fronts, even in the presence of intense Lyman-Werner flux. The high post- front
gas temperatures associated with He ionization sustained and exacerbated shadow
instabilities, unaided by molecular hydrogen cooling. Our models indicate that
metals eclipsed H2 cooling in I-front instabilities at modest concentrations,
from 0.001- 0.01 solar. We conclude that ionization front instabilities were
prominent in the H II regions of the first stars and galaxies, influencing the
escape of ionizing radiation and metals into the early universe.Comment: 13 pages, 11 figures, accepted by ApJ with minor revision
Achieving Extreme Resolution in Numerical Cosmology Using Adaptive Mesh Refinement: Resolving Primordial Star Formation
As an entry for the 2001 Gordon Bell Award in the "special" category, we
describe our 3-d, hybrid, adaptive mesh refinement (AMR) code, Enzo, designed
for high-resolution, multiphysics, cosmological structure formation
simulations. Our parallel implementation places no limit on the depth or
complexity of the adaptive grid hierarchy, allowing us to achieve unprecedented
spatial and temporal dynamic range. We report on a simulation of primordial
star formation which develops over 8000 subgrids at 34 levels of refinement to
achieve a local refinement of a factor of 10^12 in space and time. This allows
us to resolve the properties of the first stars which form in the universe
assuming standard physics and a standard cosmological model. Achieving extreme
resolution requires the use of 128-bit extended precision arithmetic (EPA) to
accurately specify the subgrid positions. We describe our EPA AMR
implementation on the IBM SP2 Blue Horizon system at the San Diego
Supercomputer Center.Comment: 23 pages, 5 figures. Peer reviewed technical paper accepted to the
proceedings of Supercomputing 2001. This entry was a Gordon Bell Prize
finalist. For more information visit http://www.TomAbel.com/GB
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