Description:

Abstract: Pulsar timing arrays search for low-frequency gravitational waves by analyzing the radio waves from millisecond pulsars distributed throughout the galaxy.  In the NANOGrav collaboration, we have recently identified a nanohertz signal that is consistent with the stochastic gravitational wave (GW) background produced by the ensemble of supermassive black hole (SMBH) binaries across the Universe.  If this signal is confirmed, it would be the first definitive proof that such systems are able to form and eventually merge.  I will discuss the wealth of physical processes that we can explore through the measurement and characterization of these low-frequency GWs.  SMBH binaries are also promising multimessenger sources as active galactic nuclei, and a large number of binary candidates have already been identified in electromagnetic surveys.  I will present the prospects for confirming these candidates, and argue for the unique discoveries made possible by simultaneous GW and EM observations.  Finally I will describe the new generation of cosmological simulations that our team is developing to tackle the challenges of high-redshift SMBH observations with JWST and the LISA mission.

Speaker: Luke Kelley, Northwestern University