Resonances in binary extreme mass ratio inspirals

TL;DR

This paper investigates how stellar-mass binaries near supermassive black holes excite black hole modes, revealing complex resonant energy flux patterns and mode excitations that depend on binary position, frequency, and black hole spin.

Contribution

It provides a detailed analysis of resonant excitation of SMBH modes by nearby binaries, highlighting the dependence on orbital parameters and black hole spin, and identifying conditions for maximal energy flux.

Findings

Resonant energy flux peaks near but not exactly at quasinormal-mode frequencies.

Offset from mode frequency increases as binary moves farther from SMBH.

Binary can excite specific SMBH oscillation modes, especially near the light ring.

Abstract

Stellar-mass binaries evolving in the vicinity of supermassive black holes (SMBHs) may be common in the universe, either in active galactic nuclei or in other astrophysical environments. Here, we study in detail the resonant excitation of SMBH modes driven by a nearby stellar-mass binary. The resulting resonant energy fluxes vary with the orbital location and frequency of the binary, exhibiting a rich and complex structure. In particular, we find that the total energy flux radiated to infinity is maximized at a gravitational-wave frequency that is close to, but not exactly equal to, the real part of the corresponding quasinormal-mode frequency. Moreover, as the binary is moved farther away from the SMBH, this offset from the mode frequency becomes increasingly pronounced. In addition, for suitable orientations, the binary can effectively ``feed'' the light ring of the SMBH, selectively exciting particular oscillation modes. For rotating (Kerr) black holes, the mode spectrum is significantly more intricate; however, individual modes are also less strongly damped, leading to an enhanced -- but more difficult to interpret -- resonant response.