Broad search for gravitational waves from subsolar-mass binaries through LIGO and Virgo's third observing run

Abstract

We present a search for gravitational waves from the coalescence of binaries which contain at least one subsolar-mass component using data from the LIGO and Virgo observatories through the completion of their third observing run. The observation of a merger with a component below 1 M would be a clear sign of either new physics or the existence of a primordial black hole population; these black holes could also contribute to the dark matter distribution. Our search targets binaries where the primary has mass M1 between 0.1 and 100 M and the secondary has mass M2 from 0.1 to 1 M for M1<20 M and 0.01 to 1 M for M1≥20 M. Sources with M1<7 M, M2>0.5 M are also allowed to have orbital eccentricity up to e10∼0.3. This search region covers from comparable to extreme mass ratio sources up to 104:1. We find no statistically convincing candidates and so place new upper limits on the rate of mergers; our analysis sets the first limits for most subsolar sources with 7M 20 M (M1<7 M). Using these limits, we constrain the dark matter fraction to below 0.3(0.7)% for 1 (0.5) M black holes assuming a monochromatic mass function. Due to the high merger rate of primordial black holes beyond the individual source horizon distance, we also use the lack of an observed stochastic background as a complementary probe to limit the dark matter fraction. We find that although the limits are, in general, weaker than those from the direct search, they become comparable at 0.1 M.