Observable Signatures of a Black Hole Ejected by Gravitational-Radiation Recoil in a Galaxy Merger

According to recent simulations, the coalescence of two spinning black holes (BHs) could lead to a BH remnant with recoil speeds of up to thousands of km s^-1. Here we examine the circumstances resulting from a gas-rich galaxy merger under which the ejected BH would carry an accretion disk and be observable. As the initial BH binary emits gravitational radiation and its orbit tightens, a hole is opened in the disk which delays the consumption of gas prior to the eventual BH ejection. The punctured disk remains bound to the ejected BH within the region where the gas orbital velocity is larger than the ejection speed. For a ∼10⁷M_⊙ BH the ejected disk has a characteristic size of tens of thousands of Schwarzschild radii and an accretion lifetime of ∼10⁷   yr. During that time, the ejected BH could traverse a considerable distance and appear as an off-center quasar with a feedback trail along the path it left behind.