http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.201301 Did LIGO Detect Dark Matter? ABSTRACT We consider the possibility that the black-hole (BH) binary detected by LIGO may be a signature of dark matter. Interestingly enough, there remains a window for masses 20M⊙≲Mbh≲100M⊙ where primordial black holes (PBHs) may constitute the dark matter. If two BHs in a galactic halo pass sufficiently close, they radiate enough energy in gravitational waves to become gravitationally bound. The bound BHs will rapidly spiral inward due to the emission of gravitational radiation and ultimately will merge. Uncertainties in the rate for such events arise from our imprecise knowledge of the phase-space structure of galactic halos on the smallest scales. Still, reasonable estimates span a range that overlaps the 2–53Gpc−3yr−1 rate estimated from GW150914, thus raising the possibility that LIGO has detected PBH dark matter. PBH mergers are likely to be distributed spatially more like dark matter than luminous matter and have neither optical nor neutrino counterparts. They may be distinguished from mergers of BHs from more traditional astrophysical sources through the observed mass spectrum, their high ellipticities, or their stochastic gravitational wave background. Next-generation experiments will be invaluable in performing these tests. Please Register or Log in to view the hidden image! Please Register or Log in to view the hidden image!
Images Please Register or Log in to view the hidden image! Figure 1 The PBH merger rate per halo as a function of halo mass. The solid line shows the trend assuming the concentration-mass relation from Ref. [27], and the dashed line from Ref. [26]. To guide the eye, the dot-dashed line shows a constant BH merger rate per unit halo mass. Reuse & Permissions Please Register or Log in to view the hidden image! Figure 2 The total PBH merger rate as a function of halo mass. Dashed and dotted lines show different prescriptions for the concentration-mass relation and halo mass function.
