Tests of Dark MACHOs: lensing, accretion, and glow

Abstract

Dark matter could take the form of dark massive compact halo objects (dMACHOs); i.e., composite objects that are made up of dark-sector elementary particles, that could have a macroscopic mass from the Planck scale to above the solar mass scale, and that also admit a wide range of energy densities and sizes. Concentrating on the gravitational interaction of dMACHOs with visible matter, we map out the mass-radius parameter space that is consistent with gravitational lensing experiments, as well as anisotropies of the cosmic microwave background (CMB) based on the spherical accretion of matter onto a dMACHO in the hydrostatic approximation. For dMACHOs with a uniform-density mass profile and total mass in the range of ∼ 10−12–10 M⊙, we find that a dMACHO could explain 100% of the dark matter if its radius is above ≈ 3 times the Einstein radius of the lensing system. For a larger mass above 10 M⊙, a dMACHO with radius above ∼ 1 × 108 cm ×(M/100 M⊙)9/2 is consistent with CMB observables. For a lighter dMACHO with mass below ∼ 10−12 M⊙, there still is not a good experimental probe. Finally, we point out that heavier dMACHOs with masses ∼ 0.1 M⊙ may be observed by X-ray and optical telescopes if they reside at rest in a large molecular cloud, nearby to our solar system, and accrete ordinary matter to emit photons.