Collaborative Research: Massive Black Hole Binaries as Multimessenger Sources: The X-ray Counterparts to Gravitational Wave Emission

This project will advance our understanding of massive back holes. Its primary focus is on massive black hole binaries (MBHBs) that inspiral toward merger due to the emission of gravitational waves (GWs). Their existence is anticipated but is yet to be definitively confirmed in observations. The discovery of such binaries would allow us to learn about their host galaxies and test some fundamental laws of physics. The project will also benefit society through innovations in teaching and learning and research training of undergraduate and graduate students. This award advances the goals of the Windows on the Universe Big Idea. In anticipation of imminent multimessenger observations of MBHBs inspiraling toward coalescence this team proposes to model the X-ray counterparts to their GW signal. The main goals of this work are: (a) to lay the groundwork for observations of this type, (b) to investigate correlations between the X-ray and GW signatures, and (c) to characterize the properties of MBHBs using both messengers. This work will result in predictions about the time-dependent photometric and spectroscopic X-ray signatures associated with inspiraling massive black hole binaries. These predictions will help guide observational strategy in X-rays in years leading to gravitational wave detections. They will be directly tested once a detection of an inspiraling binary is made, making such observations an essential ingredient in understanding one of the key phenomena in modern astrophysics. This work is relevant for the current and future X-ray observatories (XMM-Newton, Chandra, XRISM, Athena, Lynx, STROBE-X, AXIS and others) and gravitational wave observatories, such as the Pulsar Timing Arrays (PTAs) and the Laser Interferometer Space Antenna (LISA). 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.