Probing Intermediate Mass Black Holes in M87 through Multi-Wavelength Gravitational Wave Observations

Abstract

We analyze triple systems composed of the super massive black hole (SMBH) near the center of M87 and a pair of black holes (BHs) with masses in the range $10-10^3$ $M_{\odot}$. We consider the post Newtonian precession as well as the Kozai-Lidov interactions at the quadruple and octupole levels in modeling the evolution of binary black hole (BBH) under the influence of the SMBH. Kozai-Lidov oscillations enhance the gravitational wave (GW) signal in some portions of the parameter space. We identify frequency peaks and examine the detectability of GWs with LISA as well as future observatories such as $\mu$Ares and DECIGO. We show examples in which GW signal can be observed with a few or all of these detectors. Multi-Wavelength GW spectroscopy holds the potential to discover stellar to intermediate mass BHs near the center of M87. We estimate the rate, $\Gamma$, of collisions between the BBHs and flyby stars at the center of M87. Our calculation suggests $\Gamma < 10$ $\rm{Gyr}^{-1}$ for a wide range of the mass and semi-major axes of the inner binary.