Can LISA Resolve Black Hole Binaries in the M87 Globular Clusters?

Abstract

Abstract As stellar black holes (BHs) interact with one another in globular clusters, BH binaries form, inspiral, and merge via gravitational wave emission. These dynamically formed BH binaries may account for a fraction of the sources observed by LIGO/Virgo and, earlier in their inspirals, may be detected at millihertz frequencies by LISA in nearby galaxies. M87, known to contain over 104 globular clusters, is a promising candidate for such millihertz sources. Utilizing N-body cluster simulations, we investigate the binary BH population in M87 clusters. Although thousands of sources in LISA’s frequency range (10−5–1 Hz) are expected in M87's clusters, we predict none are resolvable with sufficiently high signal-to-noise ratios. We predict the nearest globular clusters in the Milky Way and clusters found in distant galaxies (d ≳ 100 Mpc) near LISA’s detection horizon for stellar BH binaries are more promising hosts of resolvable LISA sources.