1 research outputs found
First Stars. I. Evolution without mass loss
The first generation of stars was formed from primordial gas. Numerical
simulations suggest that the first stars were predominantly very massive, with
typical masses M > 100 Mo. These stars were responsible for the reionization of
the universe, the initial enrichment of the intergalactic medium with heavy
elements, and other cosmological consequences. In this work, we study the
structure of Zero Age Main Sequence stars for a wide mass and metallicity range
and the evolution of 100, 150, 200, 250 and 300 Mo galactic and pregalactic Pop
III very massive stars without mass loss, with metallicity Z=10E-6 and 10E-9,
respectively. Using a stellar evolution code, a system of 10 equations together
with boundary conditions are solved simultaneously. For the change of chemical
composition, which determines the evolution of a star, a diffusion treatment
for convection and semiconvection is used. A set of 30 nuclear reactions are
solved simultaneously with the stellar structure and evolution equations.
Several results on the main sequence, and during the hydrogen and helium
burning phases, are described. Low metallicity massive stars are hotter and
more compact and luminous than their metal enriched counterparts. Due to their
high temperatures, pregalactic stars activate sooner the triple alpha reaction
self-producing their own heavy elements. Both galactic and pregalactic stars
are radiation pressure dominated and evolve below the Eddington luminosity
limit with short lifetimes. The physical characteristics of the first stars
have an important influence in predictions of the ionizing photon yields from
the first luminous objects; also they develop large convective cores with
important helium core masses which are important for explosion calculations.Comment: 17 pages, 24 figures, 2 table