The dynamically inferred dark halo mass density, amounting to above 0.01 solar masses/cu pc at the sun's Galactocentric radius, can be composed of faint white dwarfs provided that the halo formed in a sufficiently early burst of star formation. The model is constrained by the observed disk white dwarf luminosity function which falls off below log (L/solar L) = -4.4, due to the onset of star formation in the disk. By using a narrow range for the initial mass function and an exponentially decaying halo star formation rate with an e-folding time equal to the free-fall time, all the halo dark matter is allowed to be in cool white dwarfs which lie beyond the falloff in the disk luminosity function. Although it is unlikely that all the dark matter is in these dim white dwarfs, a definite signature in the low-luminosity end of the white dwarf luminosity function is predicted even if they comprise only 1 percent of the dark matter. Current CCD surveys should answer the question of the existence of this population within the next few years.
[Show abstract][Hide abstract] ABSTRACT: A large fraction of the baryons in the universe must be dark, and
invisible baryons could at least account for the dark matter in galactic
halos. In this case, most of the baryons have been processed through
Population III stars and must now be contained in brown dwarfs or black
holes. Evidence for the first possibility may come from cluster cooling
flows; evidence for the second may come from recently detected
distortions in the spectrum of the microwave background. On the other
hand, if galactic halos are made of particle relicts from the Big Bang,
the dark baryons must be in the form of hot intergalactic gas.
[Show abstract][Hide abstract] ABSTRACT: White dwarf interiors are made of a mixture of carbon, oxygen and other
minor species, 22Ne being the most abundant one. In this
Letter we compute a preliminary phase diagram for the C-Ne and O-Ne
mixtures and we show that 22Ne can settle down at the center
as an outcome of solidification. The gravitational energy released by
this process keeps the white dwarf warm for 2 Gyr, thus delaying the
cooling process by a similar amount.
Astronomy and Astrophysics 12/1990; 241:L29-L32. · 4.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Halo dark matter, if it is baryonic, may plausibly consist of compact stellar remnants. Jeans mass clouds containing 10(6) to 10(8) solar masses could have efficiently formed stars in the early universe and could plausibly have generated, for a suitably top-heavy stellar initial mass function, a high abundance of neutron stars as well as a small admixture of long-lived low mass stars. Within the resulting clusters of dark remnants, which eventually are tidally disrupted when halos eventually form, captures of neutron stars by non-degenerate stars resulted in formation of close binaries. These evolve to produce, by the present epoch, an observable x-ray signal associated with dark matter aggregations in galaxy halos and galaxy cluster cores.
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