Unexpectedly Weak General Relativistic Effects in Strongly Relativistic Tidal Disruption Events

TL;DR

This study uses relativistic hydrodynamic simulations to show that strong relativistic effects in tidal disruption events do not lead to rapid disk formation, with debris remaining eccentric and shocks being the main energy source.

Contribution

It demonstrates that relativistic effects have a limited impact on debris evolution in TDEs, challenging previous assumptions about prompt disk formation.

Findings

Debris remains highly eccentric with most mass near apocenter.

Shocks last only about a week, dissipating orbital energy.

Stream self-interactions increase angular momentum, weakening relativistic effects.

Abstract

Tidal disruption events (TDEs) occur when stars are destroyed by supermassive black holes and are among the brightest nuclear transients. It has been thought that strong relativistic effects rapidly dissipate orbital energy and produce prompt disk formation when the stellar pericenter is smaller than $\sim 10$ gravitational radii. Using a general relativistic hydrodynamic simulation of a strongly relativistic TDE involving a Sun-like star and a $10^{6}\,M_{\odot}$ non-spinning black hole, we find instead that the overall evolution is similar to weakly relativistic TDEs: the debris remains highly eccentric, with most of the returned mass residing near the orbital apocenter ($\sim 250\times$ the initial pericenter distance), and shocks, rather than accretion, power the event. The simulation starts from the initial stellar approach and follows the debris evolution up to $35$\,days after the peak mass-return time ($\simeq$ $23$\,days). Although early shocks driven by strong relativistic apsidal precession and pericenter nozzle compression dissipate orbital energy efficiently, they last only about a week ($\sim 0.3$ of the peak mass-return time). Stream self-interactions increase the incoming stream's angular momentum, thereby expanding its pericenter distance, weakening precession and shocks, and reducing dissipation. These results suggest that circularization in TDEs may proceed slowly regardless of the strength of apsidal precession, with the flow remaining highly eccentric and extended during the peak optical/UV luminosity.