Supermassive black hole (SMBH) binaries are the primary targets of low-frequency gravitational wave (GW) experiments from space and from the ground. They are expected to be produced during collisions between galaxies carrying their own nuclear SMBHs.
I will argue that compact, gravitationally bound SMBH binaries should often be surrounded by plasma and produce bright electromagnetic (EM) emission. Hydrodynamical simulations of BH binaries with circumbinary accretion disks have revealed that the BHs can be fueled efficiently, with the fueling rates quasi-periodically modulated all the way to the BH merger. The corresponding EM emission is time-variable, with a periodicity pattern depending on the mass ratio of the BHs, and will contain unique spectral signatures. A post-merger afterglow is also expected, following the burst of GWs which drive shocks through the circumbinary plasma.
These effects may be used to identify unique EM counterparts of the GW sources expected to be discovered by Pulsar Timing Arrays (PTAs) and by the space interferometer LISA, and to discover wider binary SMBHs in time-domain EM surveys. The simultaneous EM and GW detections of SMBH binaries will enable a range of new science, from accretion physics to novel tests of gravity and dark energy.
Professor Zoltan Haiman received a Physics B.S. degree from MIT, and he attended graduate school in Cambridge, UK, and at Harvard University, where he received a Ph.D. in Astronomy in 1998. He was chosen as one of Popular Science Magazine's Brilliant 10 young scientists in 2002 and received the New York Academy of Sciences Blavatnik Award in 2010 and a Simons Fellowship in Theoretical Physics in 2016. He was a Hubble Fellow at Princeton and a postdoc in the theory group at Fermilab, before joining the Columbia faculty.
Professor Haiman's research has explored broad topics in theoretical astrophysics and cosmology, including the formation of the first stars and black holes, the subsequent growth of black holes by accretion and mergers, determining the nature of dark energy and dark matter using large astronomical surveys, as well as astrophysical sources of gravitational waves. He is currently serving as a board-appointed member of the LISA Science Group, and a NASA-appointed member of the NASA LISA Study Team, responsible for gravitational wave astrophysics.