Title:  Binary Massive Black Holes, Active Galactic Nuclei, and Gravitational Waves

Abstract:  Black holes are the brightest, most massive, and most energetic sources in the Universe.  Massive black holes (MBHs), which are up to many billions of times more massive than our sun, are believed to shape the fate of entire galaxies.  How these behemoths form and grow in the early Universe, and how they couple to their host galaxies, remains a mystery. Following galaxy mergers, pairs of MBHs can form binaries which produce low-frequency gravitational waves (GWs) that will soon be detectable by pulsar timing arrays, like NANOGrav.  I have developed models that represents the most advanced and comprehensive simulations available for studying MBH binaries, their host galaxy interactions, and the GWs they produce. In this talk, I will describe my predictions for both GW and electromagnetic signatures, and highlight how I am using these models to explore the unique discovery space opened up by multimessenger (GW + electromagnetic) astrophysics. Excitingly, we may soon be able to test these predictions for the first time: within the NANOGrav collaboration we recently identified a nanohertz signal that is consistent with the first hints of low-frequency GWs.  As the chair of NANOGrav's astrophysics working group, I am leading the development of a comprehensive framework for predicting and interpreting the upcoming GW and electromagnetic signatures.  In a separate effort, we are developing a new generation of cosmological simulations to model the high-redshift MBHs that will soon be observable with JWST, and eventually with the space-based LISA mission.  I will highlight how my research program will leverage these detections to finally reveal how MBHs form in the early Universe and co-evolve with galaxies over cosmic time.

Seminar starts at 3:45pm and will be held in 538 Davey and virtually via Zoom: https://psu.zoom.us/j/92637070419