The Mass Fallback Rate of the Debris in Relativistic Stellar Tidal Disruption Events

Abstract

Highly energetic stellar tidal disruption events (TDEs) provide a way to study black hole characteristics and their environment. We simulate TDEs with the Phantom code in a general relativistic and Newtonian description of a supermassive black hole’s gravity. Stars, which are placed in parabolic orbits with different β parameters, are constructed with the stellar evolution code MESA and therefore have realistic stellar density profiles. We study the mass fallback rate of the debris $\dot{M}$ and its dependence on β , stellar mass, and age as well as the supermassive black hole’s spin and the choice of the gravity description. We calculate the peak value ${\dot{M}}_{\mathrm{peak}}$ , time to peak t _peak , duration of the super-Eddington phase t _Edd , time ${t}_{\gt 0.5{\dot{M}}_{\mathrm{peak}}}$ during which $\dot{M}\gt 0.5{\dot{M}}_{\mathrm{peak}}$ , early rise-time τ _rise , and late-time slope n _∞ . We recover the trends of ${\dot{M}}_{\mathrm{peak}}$ , t _peak , τ _rise , and n _∞ with β , stellar mass, and age which were obtained in previous studies. We find that t _Edd , at a fixed β , scales primarily with the stellar mass, while ${t}_{\gt 0.5{\dot{M}}_{\mathrm{peak}}}$ scales with the compactness of stars. The effect of the SMBH’s rotation depends on the orientation of its rotational axis relative to the direction of the stellar motion in the initial orbit. Encounters in prograde orbits result in narrower $\dot{M}$ curves with higher ${\dot{M}}_{\mathrm{peak}}$ , while the opposite occurs for retrograde orbits. We find that disruptions, at the same pericenter distance, are stronger in a relativistic tidal field than in a Newtonian one. Therefore, relativistic $\dot{M}$ curves have higher ${\dot{M}}_{\mathrm{peak}}$ , and shorter t _peak and t _Edd .

Keywords

• Black hole physics
• Hydrodynamical simulations
• Relativistic fluid dynamics
• Tidal disruption