MACHOs, White Dwarfs, and the Age of the Universe

Abstract

(Abridged Abstract) A favored interpretation of recent microlensing measurements towards the Large Magellanic Cloud implies that a large fraction (i.e. 10--50%) of the mass of the galactic halo is composed of white dwarfs. We compare model white dwarf luminosity functions to the data from the observational surveys in order to determine a lower bound on the age of any substantial white dwarf halo population (and hence possibly on the age of the Universe). We compare various theoretical white dwarf luminosity functions, in which we vary hese three parameters, with the abovementioned survey results. From this comparison, we conclude that if white dwarfs do indeed constitute more than 10% of the local halo mass density, then the Universe must be at least 10 Gyr old for our most extreme allowed values of the parameters. When we use cooling curves that account for chemical fractionation and more likely values of the IMF and the bolometric correction, we find tighter limits: a white dwarf MACHO fraction of 10% (30%) requires a minimum age of 14 Gyr (15.5 Gyr). Our analysis also indicates that the halo white dwarfs almost certainly have helium-dominated atmospheres.

arXiv commentFinal version accepted for publication, straight TeX formate, 6 figs, 22 pages

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Cited by in corpus (14)

• Cooling Models for Old White Dwarfs
• A Determination of the Local Density of White Dwarf Stars
• Pure hydrogen atmosphere for very cool white dwarfs
• Cooling sequences and color-magnitude diagrams for cool white dwarfs with hydrogen-atmospheres
• Mirror Dark Matter and Core Density of Galaxies
• Mirror Matter MACHOs
• Monte Carlo simulations of the halo white dwarf population
• A Survey for Faint Stars of Large Proper Motion Using Extra Poss II Plates
• No nearby counterparts to the moving objects in the Hubble Deep Field
• Axionic Boson Stars in Magnetized Conducting Media
• Constraining the cosmic abundance of stellar remnants with multi-TeV gamma-rays
• Energy Dissipation of Axionic Boson Stars in Magnetized Conducting Media
• Neutron Stars and Black Holes as MACHOs
• The Observational Signature of Old White Dwarfs