Possibility of primordial black holes as the source of gravitational wave events in the advanced LIGO detector

The analysis of gravitational wave (GW) data from advanced LIGO provides the mass of each companion of binary black holes as the source of GWs. The mass of events corresponding to the binary black holes from GW is above $20M_{\odot }$ which is much larger than the mass of astrophysical black holes detected by x-ray observations. In this work, we examine primordial black holes (PBHs) as the source of LIGO events. Assuming that 100% of the dark matter is made of PBHs, we estimate the rate at which these objects make binaries, merge, and produce GWs as a function of the redshift. The gravitational lensing of GWs by PBHs can also enhance the amplitude of the strain. We simulate GWs sourced by binary PBHs, with the detection threshold of $S/N>10$ for both Livingston and Hanford detectors. For the log-normal mass function of PBHs, we generate the expected distribution of events, compare our results with the observed events, and find the best value of the mass function parameters (i.e., $M_c=25M_{\odot }$ and $\sigma =0.6$) in the log-normal mass function. Comparing the expected number of events with the number of observed ones rules out the present-Universe binary formation PBH scenario as the candidate for the source of GW events detected by LIGO.

Figure 1

The dashed line represents the total PBH merger rate per steradian per redshift per year from Eq. (4). Here, we assume that 100% of dark matter is made of PBHs. The solid-line histogram shows the redshift dependence of the efficiency of advanced LIGO with $\mathrm{SNR}>10$ detection threshold.

Figure 2

This plot assumes that the whole of dark matter is composed of PBHs (light blue). The multiplication of the optical depth $\tau (z)$ (dark blue curve) and the event rate $N(z)$ as a function of the redshift. This curve represents the rate of microlensed GWs, sourced by PBHs.

Figure 3

The number of detected events from the simulated events for source located at $z<1$, for various log-normal parameters of $\sigma$ and $M_c$ PBH mass function, assuming $f=1$.