Finite, Intense Accretion Bursts from Tidal Disruption of Stars on Bound
  Orbits
  We study accretion processes for tidally disrupted stars approaching
supermassive black holes on bound orbits, by performing three dimensional
Smoothed Particle Hydrodynamics simulations with a pseudo-Newtonian potential.
We find that there is a critical value of the orbital eccentricity below which
all the stellar debris remains bound to the black hole. For high but
sub-critical eccentricities, all the stellar mass is accreted onto the black
hole in a finite time, causing a significant deviation from the canonical
$t^{-5/3}$ mass fallback rate. When a star is on a moderately eccentric orbit
and its pericenter distance is deeply inside the tidal disruption radius, there
can be several orbit crossings of the debris streams due to relativistic
precession. This dissipates orbital energy in shocks, allowing for rapid
circularization of the debris streams and formation of an accretion disk. The
resultant accretion rate greatly exceeds the Eddington rate and differs
strongly from the canonical rate of $t^{-5/3}$. By contrast, there is little
dissipation due to orbital crossings for the equivalent simulation with a
purely Newtonian potential. This shows that general relativistic precession is
crucial for accretion disk formation via circularization of stellar debris from
stars on moderately eccentric orbits.
