Hunting intermediate-mass black holes with LISA binary radial velocity measurements

Abstract

Despite their potential role as massive seeds for quasars, in dwarf galaxy feedback, and in tidal disruption events, the observational evidence for intermediate-mass black holes (IMBHs) is scarce. LISA may observe stellar-mass black hole binaries orbiting Galactic IMBHs, and reveal the presence of the IMBH by measuring the Doppler shift in the gravitational waveform induced by the binary's radial velocity. We estimate the number of detectable Doppler shift events and we find that it decreases with the IMBH mass. A few Galactic globular clusters (including M22 and ω Centauri) may produce at least one event detectable by LISA if they harbor an IMBH at their center. We also estimate the number of expected Doppler shift events for IMBHs wandering in the Milky Way as a result of the disruption of their parent clusters. If there is at least one binary black hole orbiting around each wandering IMBH, LISA may detect tens of Doppler shift events from IMBHs wandering in our Galaxy, and produce a map of this elusive population.

Constraining the evolution of Newton's constant with slow inspirals observed from spaceborne gravitational-wave detectors

“…The high-end of the mass spectrum corresponds to intermediate-mass BHs that might be present in the Milky Way's globular clusters, see e.g., Ref. [58] for discussions about this scenario, or Ref. [59] for an example of the potential compact object population of a Galactic globular cluster.…”

A supplementary radiation-reaction force between two binaries

“…This last possibility in particular can considerably modify the dynamics of a two-body system, e.g. by inducing Kozai-Lidov oscillations [23][24][25], resonances [26][27][28] or Doppler shifts in the waveform [29][30][31][32][33][34][35][36][37][38]. From astronomical observations, many-body systems are very common in the universe [39][40][41], so that they could constitute a non-negligible fraction of the mergers observed in GW observatories [42,43].…”