21,921 research outputs found
Probing the Epoch of Early Baryonic Infall Through 21cm Fluctuations
After cosmological recombination, the primordial hydrogen gas decoupled from
the cosmic microwave background (CMB) and fell into the gravitational potential
wells of the dark matter. The neutral hydrogen imprinted acoustic oscillations
on the pattern of brightness fluctuations due to its redshifted 21cm absorption
of the CMB. Unlike CMB temperature fluctuations which probe the power spectrum
at cosmic recombination, we show that observations of the 21cm fluctuations at
z ~ 20-200 can measure four separate fluctuation modes (with a fifth mode
requiring very high precision), thus providing a unique probe of the geometry
and composition of the universe.Comment: 5 pages, 4 figures, MNRAS Letters, accepte
Cores in Dwarf Galaxies from Dark Matter with a Yukawa Potential
We show that cold dark matter particles interacting through a Yukawa
potential could naturally explain the recently observed cores in dwarf galaxies
without affecting the dynamics of objects with a much larger velocity
dispersion, such as clusters of galaxies. The velocity dependence of the
associated cross-section as well as the possible exothermic nature of the
interaction alleviates earlier concerns about strongly interacting dark matter.
Dark matter evaporation in low-mass objects might explain the observed deficit
of satellite galaxies in the Milky Way halo and have important implications for
the first galaxies and reionization.Comment: 6 pages, 2 figure
The Habitable Epoch of the Early Universe
In the redshift range 100<(1+z)<137, the cosmic microwave background (CMB)
had a temperature of 273-373K (0-100 degrees Celsius), allowing early rocky
planets (if any existed) to have liquid water chemistry on their surface and be
habitable, irrespective of their distance from a star. In the standard LCDM
cosmology, the first star-forming halos within our Hubble volume started
collapsing at these redshifts, allowing the chemistry of life to possibly begin
when the Universe was merely 10-17 million years old. The possibility of life
starting when the average matter density was a million times bigger than it is
today argues against the anthropic explanation for the low value of the
cosmological constant.Comment: 12 pages, accepted for publication in the International Journal of
Astrobiolog
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