Circularization of Tidally Disrupted Stars around Spinning Supermassive Black Holes

By K. Hayasaki, Nicholas C. Stone, Abraham Loeb. 2015

159 citations recorded by the source corpus.

We study the circularization of tidally disrupted stars on bound orbits around spinning supermassive black holes by performing three-dimensional 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 disk. 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 possible radiated energy is up to ~2*10^{52} erg for a 1 Msun star orbiting a 10^6 Msun black hole. We also find that a retrograde (prograde) black hole spin causes the shock-induced circularization timescale to be shorter (longer) than that of a non-spinning black hole in both cooling cases. The circularization timescale 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. We also discuss the relationship between our simulations and the parabolic TDEs that are characteristic of most stellar tidal disruptions.

Subfields: Astronomy and Astrophysics, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/82dd8e406425491a57cad68c8df9648640dd0fdd

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In Astronomy and Astrophysics

Citations in the corpus

A Unified Model for Tidal Disruption Events (2018, unknown): “Hydrodynamical simulations (Shiokawa et al. 2015; Bonnerot et al. 2016; Hayasaki et al. 2016) and semi-analytical studies (Dai et al. 2013, 2015; Guillochon & Ramirez-Ruiz 2015) have shown that only in certain parameter regions can fast disk assembly happen.”
Weighing Black Holes Using Tidal Disruption Events (2018, background): “In order for the luminosity to follow the fallback rate, the stellar debris that initially returns on highly eccentric orbits must circularize on a timescale that is shorter than the fallback timescale (Shiokawa et al. 2015; Bonnerot et al. 2016b; Hayasaki et al. 2016).”
PS16dtm: A Tidal Disruption Event in a Narrow-line Seyfert 1 Galaxy (2017, background): “106), where the fraction of TDEs that are delayed is & 90% due to the debris stream being easily precessed out of its original orbital plane by black hole spin effects (Hayasaki et al. 2016; Tejeda et al. 2017).”