Gravitational Radiation Driven Supermassive Black Hole Binary Inspirals as Periodically Variable Electromagnetic Sources

Understand

Supermassive black hole binaries (SMBHBs) produced in galaxy mergers are thought to complete their coalescence, below separations of r_GW=10^{-3} (M_BH/10^8 M_sun)^{3/4} pc, as their orbit decays due to the emission of gravitational waves (GWs).

• It may be possible to identify such GW-driven inspirals statistically in an electromagnetic (EM) survey for variable sources.
• A GW-driven binary spends a characteristic time T_GW at each orbital separation r_orb < r_GW that scales with the corresponding orbital time t_orb as T_GW = (const) t_orb^{8/3}.
• If the coalescing binary produces variations in the EM emission on this timescale, then it could be identified as a variable source with a characteristic period t_var = t_orb.