1996/11/22 by Andrew Gould, Gould, Andrew
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics (astro-ph) #FOS: Physical sciences #History and Developments in Astronomy #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.astro-ph/9611185
openalex publication_date 1996/11/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Star counts made with the Hubble Space Telescope (HST) probe four populations that are important for dark matter: disk, halo, bulge, and intergalactic. The disk mass function falls for masses M<0.6 Msun in sharp contrast to the rising Salpeter function usually assumed. The amount of ``observed'' disk material is therefore lower than commonly believed which implies the need for disk dark matter. Halo stars contribute no more than a few percent of the dark matter. Disk and halo together contribute no more than 10% of the observed microlensing optical depth toward the Large Magellanic Cloud. The bulge luminosity function is similar to that of the disk down to MV ~ 10. If this similarity continues to the bottom of the main sequence, the bulge microlensing events can only be explained by a large population of brown dwarfs. Intergalactic stars in the Local Group have a density lower than the local halo density by at least 10-3.5.