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 $1\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ 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 ${M}_{1}$ between 0.1 and $100\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ and the secondary has mass ${M}_{2}$ from 0.1 to $1\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ for ${M}_{1}<20\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ and 0.01 to $1\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ for ${M}_{1}\ensuremath{\ge}20\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$. Sources with ${M}_{1}<7\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$, ${M}_{2}>0.5\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ are also allowed to have orbital eccentricity up to ${e}_{10}\ensuremath{\sim}0.3$. This search region covers from comparable to extreme mass ratio sources up to ${10}^{4}:1$. 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 $7{M}_{\ensuremath{\bigodot}}<{M}_{1}<20\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ and tightens limits by $\ensuremath{\sim}8\ifmmode\times\else\texttimes\fi{}(1.6\ifmmode\times\else\texttimes\fi{})$ where ${M}_{1}>20\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ (${M}_{1}<7\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$). Using these limits, we constrain the dark matter fraction to below $0.3(0.7)%$ for 1 $(0.5)\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ 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 $0.1\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$.