Speaker
Description
Binary supermassive black holes are expected to form and merge at galactic centers. Their dynamics encode information on their formation and environments, and can be observed by low frequency gravitational-wave detectors, potentially offering a multi-messenger source. Despite this interest, no close-by (sub parsec) binaries have been confidently identified yet.
I will describe a new method to identify and characterize supermassive binaries in non-active galactic nuclei by the gravitational lensing of individual bright stars, located behind them in the host galaxy. The motion of `caustics' - regions where point-like sources become infinitely bright - due to SMBH orbit and inspiral leads to quasi-periodic lensing of starlight: The extreme lensing magnification of individual stars produces a significant variation in the host galaxies' luminosity; its lightcurve traces the orbit of the binary system and its evolution, analogous to the waveforms recorded by gravitational-wave detectors. I will discuss the phenomenology of quasi-periodic lensing by binary SMBHs, its potential for discovering binary systems and the prospects for multi-messenger observations.
