Prolonged fallback and late-time rebrightening episodes in stellar tidal disruptions as imprints of a galactic environment

Abstract

Classic models of tidal disruption events (TDEs), employing a purely Keplerian description of stellar debris dynamics, have proven remarkably successful in describing the observed emission of these transients. We extend these simple models by including the gravitational influence of a spherically symmetric mass distribution representing either a dark matter halo or the broader galactic environment, rather than treating the disruption as an isolated star-black hole encounter. We retain a minimal, fully Newtonian setup so that the role of the host galaxy remains transparent and straightforward to interpret. Within this extended model, we find that the host potential can imprint clear signatures on the light curve that lie outside the predictive scope of traditional models, such as phases of shallow decay and episodes of late-time rebrightening. These environment-driven signatures, however, emerge only on very long timescales unless the host is unrealistically ultra-compact. For most real systems, the environmental influence turns on far too late to be captured by current observations, which explains why the early evolution of TDEs occurring in typical galaxies is essentially unaffected by the host potential and why the classic models have been so successful. Only at much longer times does the broader galactic structure begin to reshape the fallback dynamics, gradually steering the system away from the canonical $t^{-5/3}$ decay. This provides an exciting opportunity for next-generation time domain surveys to extend monitoring and track late-time TDE evolution in search of delayed signals that quietly encode information about the surrounding galactic mass.