Seven hints for primordial black hole dark matter

Abstract

Seven observations point towards the existence of primordial black holes (PBH), constituting the whole or an important fraction of the dark matter in the Universe: the mass and spin of black holes detected by Advanced LIGO/VIRGO, the detection of micro-lensing events of distant quasars and stars in M31, the non-detection of ultra-faint dwarf satellite galaxies with radius below 15 parsecs, evidences for core galactic dark matter profiles, the correlation between X-ray and infrared cosmic backgrounds, and the existence of super-massive black holes very early in the Universe's history. Some of these hints are newly identified and they are all intriguingly compatible with the reconstructed broad PBH mass distribution from LIGO events, peaking on PBH mass mPBH ≈ 3M and passing all other constraints on PBH abundances. PBH dark matter also provides a new mechanism to explain the mass-to-light ratios of dwarf galaxies, including the recent detection of a diffuse galaxy not dominated by dark matter. Finally we conjecture that between 0.1% and 1% of the events detected by LIGO will involve a PBH with a mass below the Chandrasekhar mass, which would unambiguously prove the existence of PBH.

Cosmic microwave background limits on accreting primordial black holes

“…In the mean time, there are a number of other interesting astrophysical probes in that mass range. These include future measurements of the stochastic gravitational-wave background [56][57][58][59][60] and of the mass spectrum [61], redshift distribution [62], and orbital eccentricies [63] for future binary-black-hole mergers; lensing of fast radio bursts by PBHs [64]; pulsar timing [65,66]; radio/x-ray sources [67] or the cosmic infrared background [68]; the dynamics of compact stellar systems [54]; strong-lensing systems [69]; and perhaps clustering of GW events [70][71][72][73]. The conclusions of our work suggest that it will be important to pursue vigorously these alternative avenues.…”

PBH dark matter from axion inflation

“…In Sec. 4 we apply these results to inflation models described by attractors at strong coupling. We dedicate Sec.…”

“…At this point we can proceed by defining: 4) so that in the case K(φ) = 1 we recover the usual expression:…”

“…Prompted by the LIGO discovery and the lack of positive results in dedicated dark matter searches, the idea that primordial black holes (PBHs) could be (a fraction of) dark matter has recently received a lot of attention [3][4][5][6][7][8][9][10]. PBHs are formed when local over densities collapse due to their gravitational instability.…”

Constraining primordial black holes with the EDGES 21-cm absorption signal

“…The detection of gravitational waves from black holes mergers with mass Oð10ÞM ⊙ by the LIGO and VIRGO interferometers [27,28] has recently revived the interest of the community in this topic [29][30][31][32][33] (for a review see, e.g., [34]). At the present stage, the accumulated experimental data collectively constrain the fraction of PBH DM, f PBH , to be below unity [34,35], barring scenarios in which the radiation induced by PBH is strongly modified [36] or misinterpretations of the results of lensing experiments [37][38][39].…”