Counter-rotation and slow precession in aligned eccentric nuclear discs due to gravitational wave recoil kicks

Abstract

ABSTRACT The M31 nucleus contains a supermassive black hole embedded in a massive stellar disc of apsidally aligned eccentric orbits. It has recently been shown that this disc is slowly precessing at a rate consistent with zero. Here, we demonstrate using N-body methods that apsidally aligned eccentric discs can form with a significant ($\sim$0.5) fraction of orbits counter-rotating as the result of a gravitational wave recoil kick of merging supermassive black holes. Higher amplitude kicks map to a larger retrograde fraction in the surrounding stellar population, which in turn results in slow precession. We furthermore show that discs with significant counter-rotation are more stable (i.e. apsidal alignment is most pronounced and long lasting), more eccentric, and have the highest rates of stars entering the black hole’s tidal disruption radius.