Collaborative Research: Wou-MMA: Multi-Messenger Signatures of Massive Black Hole Binaries

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It has been known for many years that a black hole (BH), millions to billions of times more massive than the Sun, resides in the heart of nearly every galaxy. Over cosmic time, some of these massive BHs will come together, forming a massive black hole binary (MBHB), and eventually merge. MBHBs also accrete nearby matter, and this accretion flow has an important impact on the merger itself. A research collaboration between Georgia Institute of Technology and the University of Virginia will help to answer the question, what are the properties of accretion flows in the vicinity of coalescing massive black hole binaries? The answer to this question has direct implications for the feasibility of coincident detections of electromagnetic (EM) and gravitational wave (GW) signals from coalescences. Such detections are considered the next observational grand challenge that will provide a more complete understanding of evolution and growth of these massive objects. In anticipation of future detections by the Pulsar Timing Arrays (PTAs) and Laser Interferometer Space Antenna (LISA), this team of collaborators will investigate the coincident EM and GW signatures of MBHBs immersed in accretion flows. There are three goals of this program that are complementary to the proposed research and enabled by the investigators' roles as scientists and educators. The first is to promote diversity in STEM through direct participation of women and members of underrepresented groups. The second is to introduce innovations in teaching and learning based on ideas drawn from this project. The third will be reached through a continued commitment to public engagement and outreach. This program will also result in mentoring of one postdoctoral researcher and research training and mentoring of one graduate student. The proposed program of research centers on a suite of high-resolution simulations with the radiation-magnetohydrodynamic (RMHD) code Athena++, which will follow MBHBs as they evolve through the PTA and LISA frequency bands. The goal of this study is to set the stage for the first simulations of accreting MBHBs with radiative transfer and to predict the resulting EM counterparts (spectra and light curves) to GW signatures. Its merits include the advancement in understanding of fundamental physical processes that shape accretion onto binaries and improved multi-messenger searches for inspiraling MBHBs bound for coalescence. Findings enabled by this research program are relevant for an array of ground- and space-based observatories and several research areas within astrophysics, including the physics of compact objects, active galactic nuclei, galaxy evolution and cosmology. This project advances the goals of the NSF Windows on the Universe Big Idea.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.