Detection of IMBHs with ground-based gravitational wave observatories: A biography of a binary of black holes, from birth to death

Abstract

Even though the existence of intermediate-mass black holes (IMBHs, black holes with masses ranging between $10^{2-4}\,M_{\odot}$) has not yet been corroborated observationally, these objects are of high interest for astrophysics. Our understanding of the formation and evolution of supermassive black holes (SMBHs), as well as galaxy evolution modeling and cosmography would dramatically change if an IMBH were to be observed. From a point of view of traditional photon-based astronomy, {which relies on the monitoring of innermost stellar kinematics}, the {\em direct} detection of an IMBH seems to be rather far in the future. However, the prospect of the detection and characterization of an IMBH has good chances in lower-frequency gravitational-wave (GW) astrophysics using ground-based detectors such as LIGO, Virgo and the future Einstein Telescope (ET). We present an analysis of the signal of a system of a binary of IMBHs (BBH from now onwards) based on a waveform model obtained with numerical relativity simulations coupled with post-Newtonian calculations at the highest available order. IMBH binaries with total masses between $200-20000\,M_\odot$ would produce significant signal-to-noise ratios (SNRs) in advanced LIGO and Virgo and the ET. We have computed the expected event rate of IMBH binary coalescences for different configurations of the binary, finding interesting values that depend on the spin of the IMBHs. The prospects for IMBH detection and characterization with ground-based GW observatories would not only provide us with a robust test of general relativity, but would also corroborate the existence of these systems. Such detections should allow astrophysicists to probe the stellar environments of IMBHs and their formation processes.