Electromagnetic signature of supermassive black hole binaries that enter their gravitational-wave induced inspiral

摘要: Mergers of gas-rich galaxies lead to black hole binaries that coalesce as a result dynamical friction on the ambient gas. Once binary tightens $\ensuremath{\lesssim}{10}^{3}$ Schwarzschild radii, its merger is driven by emission gravitational waves (GWs). We show this transition occurs generically at orbital periods $\ensuremath{\sim}1\char21{}10\text{ }\text{ }\mathrm{years}$ and an velocity $v$ few thousand $\mathrm{km}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, with very weak dependence supply rate gas ($v\ensuremath{\propto}{\stackrel{\ifmmode \dot{}\else \textperiodcentered \fi{}}{M}}^{1/8}$). Therefore, enter their GW-dominated inspiral, they inevitably induce large periodic shifts in broad lines any associated quasar(s). The probability finding tighter configurations scales ${v}^{\ensuremath{-}8}$ owing much shorter lifetimes. Narrow-band monitoring quasars time months decades can set lower limit expected GW sources for Laser Interferometer Space Antenna.