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 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 M ̇ peak , time to peak t peak, duration of the super-Eddington phase t Edd, time t > 0.5 M ̇ peak during which M ̇ > 0.5 M ̇ peak , early rise-time τ rise, and late-time slope n ∞. We recover the trends of M ̇ 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 > 0.5 M ̇ 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 M ̇ curves with higher M ̇ 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 M ̇ curves have higher M ̇ peak , and shorter t peak and t Edd.

The Peak of the Fallback Rate from Tidal Disruption Events: Dependence on Stellar Type

“…Goicovic et al (2019) and Golightly et al (2019) found that the disruption of a 1 M e star at zero-age main sequence (ZAMS; evolved with the stellar evolution code MESA; Paxton et al 2011) yielded a peak fallback time of ∼25 days, as compared to the frozen-in prediction of ∼1 yr (see Figure 5 in Goicovic et al 2019 and Figure 2 in Golightly et al 2019). Similar results have been found by, for example, Law-Smith et al (2019, Ryu et al (2020a), andJankovič &Gomboc (2023), and some aspects of this problem have been reviewed by Wevers & Ryu (2023). Coughlin & Nixon (2022a) suggested that the discrepancy is at least partially related to the definition of the tidal radius, and in particular they noted that a star should be completely destroyed when the tidal field of the black hole exceeds the maximum self-gravitational field within the star.…”