Extreme Mass Ratio Inspirals triggered by Massive Black Hole Binaries: from Relativistic Dynamics to Cosmological Rates

Abstract

Extreme mass ratio inspirals (EMRIs) are compact binary systems characterized by a mass-ratio $q=m/M$ in the range $10^{-9}-10^{-4}$ and represent primary gravitational wave (GW) sources for the forthcoming Laser Interferometer Space Antenna (LISA). While their standard formation channel involves relaxation processes deflecting compact objects on very low angular momentum orbits around the central massive black hole, a number of alternative formation channels has been proposed, including binary tidal break-up, migration in accretion disks and secular and chaotic dynamics around a massive black hole binary (MBHB). In this work, we take an extensive closer look at this latter scenario, investigating how EMRIs can be triggered by a MBHBs, formed in the aftermath of galaxy mergers. By employing a suite of relativistic three-body simulations, we evaluate the efficiency of EMRI formation for different parameters of the MBHB, assessing the importance of both secular and chaotic dynamics. By modelling the distribution of compact objects in galaxy nuclei, we estimate the resulting EMRI formation rate, finding that EMRI are produced in a sharp burst, with peak rates that are 10-100 times higher than the standard two-body relaxation channel, lasting for 10${}^6$--10${}^8$ years. By coupling our results with an estimate of the cosmic MBHB merger rate, we finally forecast that LISA could observe $\mathcal{O}(10)$ EMRIs per year formed by this channel.

18 pages, 15 figures, accepted for publication in MNRAS

References in corpus (7)

• Intermediate and Extreme Mass-Ratio Inspirals -- Astrophysics, Science Applications and Detection using LISA
• Starbursts near supermassive black holes: young stars in the Galactic Center, and gravitational waves in LISA band
• Stellar remnants in galactic nuclei: mass segregation
• Interaction of massive black hole binaries with their stellar environment: I. Ejection of hypervelocity stars
• The imprint of massive black hole formation models on the LISA data stream
• Gravitational wave cosmology with extreme mass-ratio inspirals
• Tidal Disruption of Stellar Objects by Hard Supermassive Black Hole Binaries