Circularization of tidally disrupted stars around spinning supermassive black holes

Kimitake Hayasaki, Nicholas Stone, Abraham Loeb

Research output: Contribution to journalArticlepeer-review

Abstract

We study the circularization of tidally disrupted stars on bound orbits around spinning supermassive black holes by performing 3D smoothed particle hydrodynamic simulations with post-Newtonian corrections. Our simulations reveal that debris circularization depends sensitively on the efficiency of radiative cooling. There are two stages in debris circularization if radiative cooling is inefficient: first, the stellar debris streams self-intersect due to relativistic apsidal precession; shocks at the intersection points thermalize orbital energy and the debris forms a geometrically thick, ring-like structure around the black hole. The ring rapidly spreads via viscous diffusion, leading to the formation of a geometrically thick accretion disc. In contrast, if radiative cooling is efficient, the stellar debris circularizes due to self-intersection shocks and forms a geometrically thin ring-like structure. In this case, the dissipated energy can be emitted during debris circularization as a precursor to the subsequent tidal disruption flare. The circularization time-scale is remarkably long in the radiatively efficient cooling case, and is also sensitive to black hole spin. Specifically, Lense-Thirring torques cause dynamically important nodal precession, which significantly delays debris circularization. On the other hand, nodal precession is too slow to produce observable signatures in the radiatively inefficient case. Since the stellar debris is optically thick and its photon diffusion time is likely longer than the time-scale of shock heating, our inefficient cooling scenario is more generally applicable in eccentric tidal disruption events (TDEs). However, in parabolic TDEs for MBH ≳ 2 × 106M, the spin-sensitive behaviour associated with efficient cooling may be realized.

Original languageAmerican English
Pages (from-to)3760-3780
Number of pages21
JournalMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume461
Issue number4
DOIs
StatePublished - 1 Oct 2016
Externally publishedYes

Keywords

  • Accretion
  • Black hole physics
  • Gravitational waves
  • Hydrodynamics
  • accretion discs

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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