Binary and triple systems of supermassive black holes in galactic nuclei
Abstract
Galaxies with stellar bulges are generically observed to host supermassive black holes (SMBHs),
and the hierarchical merging of galaxies therefore leads to the formation of SMBH binaries. In the
low-density, gas-poor nuclei of giant elliptical galaxies, these binaries are expected to survive over
times much longer than a Hubble time, leading to the formation of triple SMBH systems. I will discuss
the dynamics of binary and triple SMBH systems in the stellar environments typical of elliptical galaxies,
as well as the signatures of these systems in forthcoming pulsar timing experiments designed to detect
low-frequency gravitational waves. I will highlight several open problems related to SMBH binary
evolution in galactic nuclei, including the eccentricity evolution of strongly bound binaries and the effect
of triaxiality of the stellar distribution on the SMBH evolution.