Observational Signatures of Binary Supermassive Black Holes

Understand

Observations indicate that most massive galaxies contain a supermassive black hole, and theoretical studies suggest that when such galaxies have a major merger, the central black holes will form a binary and eventually coalesce.

• Here we discuss two spectral signatures of such binaries that may help distinguish them from ordinary AGN.
• These signatures are expected when the mass ratio between the holes is not extreme and the system is fed by a circumbinary disk.
• One such signature is a notch in the thermal continuum that has been predicted by other authors; we point out that it should be accompanied by a spectral revival at shorter wavelengths and also discuss its dependence on binary properties such as mass, mass ratio, and separation.