Black hole mergers in active galactic nuclei

This research falls within the RC's Particle Astrophysics Gravitational Waves research area.

The recent detections of gravitational waves by LIGO, VIRGO, and KAGRA opened a new window on the Universe, giving unprecedented observational opportunities into regions of space and time which are completely hidden to traditional electromagnetic observatories. The gravitational wave detections have shown that stellar mass black holes merge frequently in the Universe, but the astrophysical origin and host environments of these mergers is not well understood.

The objective of the project is to examine a novel possibility that may explain the gravitational wave observations. We examine the possibility that the observed stellar mass black hole mergers originate in active galactic nuclei in the vicinity of a supermassive black hole. We build numerical models of the gaseous disk surrounding a supermassive black hole and investigate how a population of stellar mass black holes in this region interact within the disk. We investigate the possibility that black holes form binaries during close encounters, and dynamical interaction of such binaries with other stars and black holes. The interplay of hydrodynamical and gravitational wave effects may lead to an efficient merger of black holes in these environments. We determine the expected rate of mergers and the characteristics of the gravitational waves from these systems, and compare the predictions of these theoretical models with the observed source population of LIGO, VIRGO, and KAGRA. We will also explore the expected implications for the LISA space mission.

The potential impact of this research is not limited to gravitational wave science but it may have applications in cosmology and planet formation. Black hole mergers in active galactic nuclei generate gravitational wave events with possible electromagnetic counterparts. If so, these sources make it possible to use them as standard candles to probe the cosmological model of the Universe. Furthermore, the dynamics of point masses in gaseous environments may also be relevant to understand the evolution of planetesimals in protoplanetary disks. The numerical methodology and theoretical framework developed for this project may be applied in the context of planet formation as well.