zandalman

When a star passes close to a supermassive black hole (BH), the BH's tidal forces rip it apart into a thin stream, leading to a tidal disruption event (TDE). In this work, we study the post-disruption phase of TDEs in general relativistic hydrodynamics (GRHD) using our GPU-accelerated code H-AMR. We carry out the first grid-based simulation of a deep-penetration TDE (beta = 7) with realistic system parameters: a black hole-to-star mass ratio of 1e6, a parabolic stellar trajectory, and a non-zero BH spin. We also carry out a simulation of a tilted TDE whose stellar orbit is inclined relative to the BH midplane. We show that for our aligned TDE, an accretion disc forms due to the dissipation of orbital energy with ~20% of the infalling material reaching the BH. The dissipation is initially dominated by violent self-intersections and later by stream-disc interactions near the pericentre. The self-intersections completely disrupt the incoming stream, resulting in five distinct self-intersection events separated by approximately 12 hours and a flaring in the accretion rate. We also find that the disc is eccentric with mean eccentricity e = 0.88. For our tilted TDE, we find only partial self-intersections due to nodal precession near pericentre. Although these partial intersections eject gas out of the orbital plane, an accretion disc still forms with a similar accreted fraction of the material to the aligned case. These results have important implications for disc formation in realistic tidal disruptions. For instance, the periodicity in accretion rate induced by the complete stream disruption may explain the flaring events from Swift J1644+57.

Contour plots of the logarithmic rest mass density in the equatorial plane during the debris’ initial pericentre passage (first row) and the first (second row) and third (third row) self-intersection events. In the initial pericentre passage, the stream falls back through near vacuum and matter from the stream begins to accumulate near the BH. In the self-intersection events, the stream undergoes apsidal precession and self-intersects close to the analytical self-intersection radius at 142 rg. As a result, the inner parts of the stream are completely disrupted. These violent events are a key dissipation mechanism in the early stages of the TDE evolution. Although powerful, we count only five such events. At late times in our simulation, dissipation occurs primarily through interactions with the newly formed disc.

Tidal Disruption Discs Formed and Fed by Stream-Stream and Stream-Disc Interactions in Global GRHD Simulations

Abstract