Email office@phys.ksu.edu for the Zoom address
Abstract
Supermassive black holes (SMBHs), with masses of millions to billions times the mass of the Sun, live in the centers of nearly all massive galaxies. When two galaxies collide, their SMBHs can spiral together and merge, which creates very powerful gravitational waves (ripples in spacetime). Gravitational waves from black hole mergers were first detected by LIGO in 2015, and the LIGO-Virgo-KAGRA collaboration has now detected nearly a hundred gravitational-wave events. An entirely different approach is required, however, to detect the nanoHertz- to milliHertz-frequency gravitational waves produced by SMBHs. Earlier this year, NANOGrav and other pulsar timing array experiments worldwide presented strong evidence for a gravitational-wave background consistent with a population of inspiraling SMBH binaries. I will summarize these results and describe how we can use a combination of theoretical models and gravitational-wave observations to infer the characteristics of the SMBH binary population. In addition, the Laser Interferometer Space Antenna (LISA), set to launch sometime next decade, will be able to detect gravitational waves from merging SMBHs throughout the observable Universe. I will discuss the prospects for LISA, pulsar timing arrays, and electromagnetic observations to reveal the origins and evolution of SMBHs in this new era of low-frequency gravitational-wave astrophysics.