colloquium – Alessandra De Rosa: The quest for dual and binary supermassive black holes

Hierarchical models of galaxy formation predict that galaxy mergers represent a key transitional stage of rapid SMBH growth; however, the lack of a census of AGN pairs over cosmic time prevents us from firmly connecting AGN triggering and merging processes.
The quest for pairs of SMBHs at the dawn of the multi-messenger era is compelling. These systems represent the natural precursor to coalescing SMBHs that are among the loudest sources of gravitational waves.  Detecting dual AGN – active SMBHs at projected separations larger than several parsecs – and binary AGN – active SMBHs  bound in a Keplerian binary – is an observational challenge.
The talk will review the observational efforts, across the electromagnetic spectrum, on the detection and study of dual and binary SMBHs and will reflect on broader implications of these findings when considering the current simulations of merging BH.