6 research outputs found
Effects of dark matter annihilation on the first stars
We study the evolution of the first stars in the universe (Population III)
from the early pre-Main Sequence until the end of helium burning in the
presence of WIMP dark matter annihilation inside the stellar structure. The two
different mechanisms that can provide this energy source are the contemporary
contraction of baryons and dark matter, and the capture of WIMPs by scattering
off the gas with subsequent accumulation inside the star. We find that the
first mechanism can generate an equilibrium phase, previously known as a "dark
star", which is transient and present in the very early stages of pre-MS
evolution. The mechanism of scattering and capture acts later, and can support
the star virtually forever, depending on environmental characteristic of the
dark matter halo and on the specific WIMP model.Comment: Proceedings of the IAU Symposium 255, "Low-Metallicity Star
Formation: From the First Stars to Dwarf Galaxies"; L.K. Hunt, S. Madden and
R. Schneider ed
First star formation with dark matter annihilation
We include an energy term based on Dark Matter (DM) self-annihilation during
the cooling and subsequent collapse of the metal-free gas, in halos hosting the
formation of the first stars in the Universe. We have found that the feedback
induced on the chemistry of the cloud does modify the properties of the gas
throughout the collapse. However, the modifications are not dramatic, and the
typical Jeans mass within the halo is conserved throughout the collapse, for
all the DM parameters we have considered. This result implies that the presence
of Dark Matter annihilations does not substantially modify the Initial Mass
Function of the First Stars, with respect to the standard case in which such
additional energy term is not taken into account. We have also found that when
the rate of energy produced by the DM annihilations and absorbed by the gas
equals the chemical cooling (at densities yet far from the actual formation of
a proto-stellar core) the structure does not halt its collapse, although that
proceeds more slowly by a factor smaller than few per cent of the total
collapse time.Comment: 12 pages, 8 figures, 3 tables; replaced with published version after
minor change
Dark matter annihilation effects on the first stars
We study the effects of WIMP dark matter (DM) on the collapse and evolution
of the first stars in the Universe. Using a stellar evolution code, we follow
the pre-Main Sequence (MS) phase of a grid of metal-free stars with masses in
the range 5-600 solar mass forming in the centre of a 1e6 solar mass halo at
redhisft z=20. DM particles of the parent halo are accreted in the
proto-stellar interior by adiabatic contraction and scattering/capture
processes, reaching central densities of order 1e12 GeV/cm3 at radii of the
order of 10 AU. Energy release from annihilation reactions can effectively
counteract the gravitational collapse, in agreement with results from other
groups. We find this stalling phase (known as "dark" star) is transients and
lasts from 2.1e3 yr (M=600 solar mass) to 1.8e4 yr (M=9 solar mass). Later in
the evolution, DM scattering/capture rate becomes high enough that energy
deposition from annihilations significantly alters the pre-MS evolution of the
star in a way that depends on DM (i) velocity dispersion, (ii) density, (iii)
elastic scattering cross section with baryons. For our fiducial set of
parameters (10 km/s, 1e11 GeV/cm3, 1e-38 cm2) we find that the evolution of
stars of mass lower than 40 solar masses "freezes" on the HR diagram before
reaching the ZAMS. Stars with bigger masses manage to ignite nuclear reactions;
however, DM "burning" prolonges their lifetimes by a factor 2 (5) for a 600
(40) solar mass star.Comment: Comments welcom
Dark Stars: A New Study of the FIrst Stars in the Universe
We have proposed that the first phase of stellar evolution in the history of
the Universe may be Dark Stars (DS), powered by dark matter heating rather than
by nuclear fusion. Weakly Interacting Massive Particles, which may be their own
antipartners, collect inside the first stars and annihilate to produce a heat
source that can power the stars. A new stellar phase results, a Dark Star,
powered by dark matter annihilation as long as there is dark matter fuel, with
lifetimes from millions to billions of years. We find that the first stars are
very bright () and cool (K) during the DS
phase, and grow to be very massive (500-1000 times as massive as the Sun).
These results differ markedly from the standard picture in the absence of DM
heating, in which the maximum mass is about 140 and the temperatures
are much hotter (K); hence DS should be observationally
distinct from standard Pop III stars. Once the dark matter fuel is exhausted,
the DS becomes a heavy main sequence star; these stars eventually collapse to
form massive black holes that may provide seeds for supermassive black holes
observed at early times as well as explanations for recent ARCADE data and for
intermediate black holes.Comment: article to be published in special issue on Dark Matter and Particle
Physics in New Journal of Physic