Constraining the Cosmic Abundance of Stellar Remnants with Multi-T[CLC]e[/CLC]V Gamma Rays

If stellar remnants are cosmologically significant, the infrared flux from the remnant progenitors would contribute to the opacity of multi-TeV γ-rays. The multi-TeV γ-ray horizon is established to be at a redshift z > 0.034 by the observation of the blazar Mrk 501. By requiring that the optical depth due to γγ → e + e - be less than 1 for a source at z = 0.034, we limit the cosmological density of stellar remnants, Ω rm ≤ (2-4) × 10 -3 h ( h 70 is the Hubble constant in units of 70 km s -1 Mpc -1 ), and thus strongly constrain stellar remnants as a cosmologically significant source of dark matter.