Disc formation from tidal disruptions of stars on eccentric orbits by Schwarzschild black holes

By C. Bonnerot, E. Rossi, G. Lodato, Daniel J. Price. 2015

174 citations recorded by the source corpus.

The potential of tidal disruption of stars to probe otherwise quiescent supermassive black holes cannot be exploited, if their dynamics is not fully understood. So far, the observational appearance of these events has been derived from analytical extrapolations of the debris dynamical properties just after disruption. By means of hydrodynamical simulations, we investigate the subsequent fallback of the stream of debris towards the black hole for stars already bound to the black hole on eccentric orbits. We demonstrate that the debris circularize due to relativistic apsidal precession which causes the stream to self-cross. The circularization timescale varies between 1 and 10 times the period of the star, being shorter for more eccentric and/or deeper encounters. This self-crossing leads to the formation of shocks that increase the thermal energy of the debris. If this thermal energy is efficiently radiated away, the debris settle in a narrow ring at the circularization radius with shock-induced luminosities of $\sim 10-10^3 \, L_{\rm Edd}$. If instead cooling is impeded, the debris form an extended torus located between the circularization radius and the semi-major axis of the star with heating rates $\sim 1-10^2 \, L_{\rm Edd}$. Extrapolating our results to parabolic orbits, we infer that circularization would occur via the same mechanism in $\sim 1$ period of the most bound debris for deeply penetrating encounters to $\sim 10$ for grazing ones. We also anticipate the same effect of the cooling efficiency on the structure of the disc with associated luminosities of $\sim 1-10 \, L_{\rm Edd}$ and heating rates of $\sim 0.1-1 \, L_{\rm Edd}$. In the latter case of inefficient cooling, we deduce a viscous timescale generally shorter than the circularization timescale. This suggests an accretion rate through the disc tracing the fallback rate, if viscosity starts acting promptly.

Subfields: Astronomy and Astrophysics, Biomedical Engineering

View Paper: https://www.semanticscholar.org/paper/4e08e8678ed888acd2b25ba73e1790191435cbc9

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Citations in the corpus

Phantom: A Smoothed Particle Hydrodynamics and Magnetohydrodynamics Code for Astrophysics (2017, methodology): “See Bonnerot et al. (2016) for a recent application.”
PS16dtm: A Tidal Disruption Event in a Narrow-line Seyfert 1 Galaxy (2017, background): “In a naked flare, a stream will continue to elongate and maintain a thin profile until it strikes itself, at which point circularization can begin at the point of collision (e.g. Bonnerot et al. 2016).”
Stellar Dynamics and Stellar Phenomena Near a Massive Black Hole (2017, background): “…of the debris streams, especially if the orbit is bound (Dai, Escala & Coppi 2013), by misaligning debris streams of different energies and enhancing the shocks as they intersect near the disruption point (Guillochon & Ramirez-Ruiz 2015; Bonnerot et al. 2016; Hayasaki, Stone & Loeb 2016).”