1999ApJ...523L..77G

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)x10^–3h^–1₇₀ (h₇₀ 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.