The two recent gravitational-wave events GW190425 and GW190814 from the third observing run of LIGO/Virgo have both a companion which is unexpected if originated from a neutron star or a stellar black hole , with masses [ 1.6 - 2.5 ] ~ { } M _ { \odot } and [ 2.5 - 2.7 ] ~ { } M _ { \odot } and merging rates 460 ^ { +1050 } _ { -360 } and 7 ^ { +16 } _ { -6 } events/yr/Gpc ^ { 3 } respectively , at 90 % c.l..
The possibility that these objects are Primordial Black Holes ( PBHs ) is investigated .
The known thermal history of the Universe predicts that the PBH formation is boosted at the time of the QCD transition , inducing a peak in their distribution at this particular mass scale , and a bump around 30 - 50 ~ { } M _ { \odot } .
We find that the merging rates inferred from GW190425 and GW190814 are consistent with PBH binaries formed by capture in dense halos or before matter-radiation equality .
At the same time , the rate of black hole mergers around 30 ~ { } M _ { \odot } and of sub-solar PBH mergers do not exceed the LIGO/Virgo limits .
Such PBHs could explain a significant fraction , or even the totality of the Dark Matter , but they must be sufficiently strongly clustered in order to be consistent with current astrophysical limits .