The merger of massive black hole binaries (MBHBs) is a mighty gravitational wave (GW) event, which will be detected by future space-based laser interferometers such as LISA. MBHBs are a natural outcome of the hierarchical process of galaxy mergers, and their coalescence may occur in a magnetized, gas-rich environment, yielding powerful electromagnetic (EM) emissions. The simultaneous observation of both GW and EM radiation emerging from such systems will provide precise measurements of cosmological parameters and help assess the evolutionary history of galaxies.
To explore the magnetohydrodynamical features of the hot plasma surrounding these systems, we produced a suite of general-relativistic magnetohydrodynamical (GRMHD) simulations of the late-inspiral and merger of MBHBs. Our work models for the first time the GRMHD evolution of merging binaries of spinning black holes, with spins either aligned or misaligned to the orbital angular momentum.
Our goal is to capture the effects of spins on the mass accretion rates, the gas dynamics, and the EM energy emitted during the late-inspiral and merger. We observe that a higher postmerger spin of the remnant black hole corresponds to lower mass accretion rates onto the horizon. In agreement with the Blandford-Znajek formula, we find that the postmerger value of the Poynting luminosity emitted by the remnant is proportional to the square of the spin parameter. In addition, we identify quasiperiodic modulations in the premerger accretion rate that evolve in parallel with the GW signal. This result could provide a valuable signature of EM emission concurrent to low-frequency GW detection, offering a novel outlook for future multimessenger astronomy.
Authors: Federico Cattorini, Bruno Giacomazzo, Francesco Haardt, Monica Colpi
Presenter: Federico Cattorini
