WoU-MMA: Multi-messenger transients from magnetically arrested accretion onto supermassive black hole binaries

Merging supermassive black hole binaries (SMBHBs) are exciting sources for gravitational wave detections with space-based gravitational wave observatories and pulsar timing arrays. Since they will likely be surrounded by a gaseous accretion flow, they can also power multi-messenger transient emission before, during and after merger. This project will investigate a novel accretion regime that could give rise to new electromagnetic detection channels of SMBHBs and their merger. The researchers will investigate the magnetically arrested (MAD) accretion regime of a SMBHB, in which the black holes are embedded in a strong magnetic field regulating the accretion flow and leading to periodic magnetic flux eruptions into the accretion disk. This project will positively contribute to the training of the STEM workforce. The junior personnel on the project will learn analytic and problem-solving techniques, including computational methods and competence with standard quantitative analysis and programming tools, which will enhance their productivity in whatever future endeavors or careers they pursue. These investigations will contribute to our understanding of future multi-messenger gravitational wave events of merging supermassive black hole binaries and their orbital evolution. This includes investigating a novel magnetically arrested (MAD) accretion regime for circumbinary accretion flows onto SMBHBs. In particular, the researchers will determine whether this regime influences the orbital dynamics (and hence the observed merging population) of SMBHB. This project will also perform galactic-scale accretion simulations (from Mpc to pc scales) to demonstrate under which condition a hypermagnetized accretion flow can form, which can support a MAD regime. Finally, they will investigate what type of multi-messenger transients a MAD circumbinary disk regime will give rise to, particularly before during and after merger. As a direct outcome, these studies will provide observable signatures for merging SMBHBs, such as recently proposed ideas on near-infrared flares after merger. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.