Periodic Reporting for period 1 - UnveilingBlackHoles (Unveiling the population of supermassive black hole binaries near merger)
Período documentado: 2021-04-01 hasta 2023-03-31
Supermassive black holes pair together at the centers of newly collided galaxies. If they eventually spiral towards one another and coalesce, they would contribute the strongest sources of gravitational waves in the universe, at frequencies which will be detectable in the near future. However, the steps between galaxy merger and black hole merger are still not understood, and while candidates exist, there is yet no definitive evidence for such supermassive binaries in the late stages of inspiral. This work has made strides towards further understanding this issue by carrying out state-of-the-art numerical hydrodynamical calculations of the interaction of these binaries with gas expected to exist at the centers of binary harbouring galaxies. Results of these calculations have been and will continue to be used to 1) improve theoretical predictions of binary populations and 2) characterise electromagnetic signatures of accreting supermassive black hole binaries with which to find these elusive pairs. Finally understanding this issue would provide further insight into the mutual growth of galaxies and black holes across cosmic time and hence provide a more complete picture of the build up of these entities as we now observe them in our universe. It will also provide necessary theoretical preparation for the coming observations of low frequency gravitational waves with experiments like the Pulsar timing arrays and the Laser Interferometer Space Antenna (LISA).
This work carried out high resolution numerical calculations of gas interacting with binaries on a wide range of possible binary orbits. The response of the binary orbit was measured over this range providing a way to model how the binary grows in mass and how its orbit decays, expands, or becomes more or less eccentric as it interacts with gas. A major result for this work is that binaries tend to be driven to a specific orbital eccentricity, which may be detectable in present (and future) observations of populations of binary systems. The numerical calculations also allowed a measure of the rate at which gas falls onto each component of the binary, hence providing a way to simulate the modulation of light coming from putative binary black hole systems as they accrete gas. The former, binary orbital response, was used to model populations and compare to data on binary star populations. The latter, simulated accretion rates, were paired with other models for emission from accreting binaries to model some observed systems. Results of the numerical calculations are continuing to be exploited for rather study and modelling. The work was disseminated in six published papers as well as 10 scientific talks.
The base suite of numerical calculations, simulating gas discs accreting onto binaries, progressed beyond the state of the art by expanding our understanding of these solutions to the entire range of binary eccentricities as well as expanding into other parameter space. This has then allowed progress beyond the state of the art in modelling binary orbital evolution, possible observational signatures, and hence predictions for discovering these systems in the near future.