Tidal Disruptions of Main-sequence Stars. III. Stellar Mass Dependence of the Character of Partial Disruptions

Abstract

In this paper, the third in this series, we continue our study of tidal disruption events of main-sequence stars by a nonspinning 10 6 M ⊙ supermassive black hole. Here we focus on the stellar mass dependence of the outcomes of partial disruptions. As the encounter becomes weaker, the debris mass is increasingly concentrated near the outer edges of the energy distribution. As a result, the mass fallback rate can deviate substantially from a t −5/3 power law, becoming more like a single peak with a tail declining as t − p with p  ≃ 2–5. Surviving remnants are spun-up in the prograde direction and are hotter than main-sequence stars of the same mass. Their specific orbital energy is ≃10 −3 × that of the debris, but of either sign with respect to the black hole potential, while their specific angular momentum is close to that of the original star. Even for strong encounters, remnants have speeds at infinity relative to the black hole potential ≲300 km s −1 , so they are unable to travel far out into the galactic bulge. The remnants most deeply bound to the black hole go through a second tidal disruption event upon their first return to pericenter; if they have not thermally relaxed, they will be completely disrupted.