Primordial Black Hole Scenario for the Gravitational-Wave Event GW150914

Abstract

We point out that the gravitational-wave event GW150914 observed by the LIGO detectors can be explained by the coalescence of primordial black holes (PBHs). It is found that the expected PBH merger rate would exceed the rate estimated by the LIGO Scientific Collaboration and the Virgo Collaboration if PBHs were the dominant component of dark matter, while it can be made compatible if PBHs constitute a fraction of dark matter. Intriguingly, the abundance of PBHs required to explain the suggested lower bound on the event rate, >2 events Gpc^{-3} yr^{-1}, roughly coincides with the existing upper limit set by the nondetection of the cosmic microwave background spectral distortion. This implies that the proposed PBH scenario may be tested in the not-too-distant future.

Production of high stellar-mass primordial black holes in trapped inflation

“…Interestingly, massive PBHs being non-relativistic and weakly interacting gravitationally may constitute the cold dark matter, if they are formed prior to the big bang nucleosynthesis. The estimated merger rate for these PBHs, if they are clustered in compact sub-halos, can span a range that overlaps the BH merger rate inferred from GW150914 [7][8][9]. As such, GW150914 can be considered as an indirect signal of dark matter coming from the PBH sub-halo that is a conversion of a few M ⊙ dark matter into gravitational waves in a massive PHB coalescence.…”

Inflationary theory and pulsar timing investigations of primordial black holes and gravitational waves

“…Already, the EPTA and PPTA experiments exclude this model of PBH formation up to masses peaked at greater than 30M ⨀ due to the contributions to SGWs at high frequency. 6 However, it is possible that critical collapse effects may still narrowly allow this model.…”

“…In addition, the merger rate observed by LIGO may be consistent with primordial black holes (PBHs) (for PBH reviews, see, e.g., Refs. [3,4]) making up all [5] or a fraction ∼10 −3 [6,7] of the observed dark matter (DM) density. In this study, we investigate the consequences for theory and experiment by assuming the PBH merger explanation.…”

Cosmic microwave background bounds on primordial black holes

“…[8] that the DM may be fully accounted by PBH of tens of solar masses-consistent with the progenitors of the mergers recently detected via gravitational waves by LIGO [9]-by now half a dozen of independent arguments have been raised, indicating that the majority of DM cannot reside in these objects. On the other hand, the possibility of a subleading fraction of DM in the form of stellar-mass PBH accounting for part or even the totality of LIGO merger rate [10,11] is still an open possibility, which makes the investigation of specific signatures particularly important in the forthcoming years.…”