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Tidal Disruption Events: The Role of Stellar Spin

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journal contribution
posted on 11.06.2019, 13:16 by Elen C. A. Golightly, Eric R. Coughlin, C. J. Nixon
The tidal force from a supermassive black hole can rip apart a star that passes close enough in what is known as a Tidal Disruption Event (TDE). Typically, half of the destroyed star remains bound to the black hole and falls back on highly eccentric orbits, forming an accretion flow that powers a luminous flare. In this paper, we use analytical and numerical calculations to explore the effect of stellar rotation on the fallback rate of material. We find that slowly spinning stars (Ω* <= 0.01Ωbreakup) provide only a small perturbation to fallback rates found in the nonspinning case. However, when the star spins faster, there can be significant effects. If the star is spinning retrograde with respect to its orbit, the tidal force from the black hole has to spin down the star first before disrupting it, causing delayed and sometimes only partial disruption events. However, if the star is spinning prograde, this works with the tidal force and the material falls back sooner and with a higher peak rate. We examine the power-law index of the fallback curves, finding that in all cases the fallback rate overshoots the canonical t^−5/3 rate briefly after the peak, with the depth of the overshoot dependent on the stellar spin. We also find that, in general, the late time evolution is slightly flatter than the canonical t^−5/3 rate. We therefore conclude that considering the spin of the star may be important in modeling observed TDE light curves.

Funding

C.J.N. is supported by the Science and Technology Facilities Council (STFC) (grant No. ST/M005917/1). E.R.C. acknowledges support from NASA through the Einstein Fellowship Program, grant PF6-170150. This research used the ALICE High Performance Computing Facility at the University of Leicester. The figures were made using splash (Price 2007), a visualization tool for SPH data. This work was performed using the DiRAC Data Intensive service at Leicester, operated by the University of Leicester IT Services, which forms part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). The equipment was funded by BEIS capital funding via STFC capital grants ST/K000373/1 and ST/R002363/1 and STFC DiRAC Operations grant ST/R001014/1. DiRAC is part of the National e-Infrastructure. Software: phantom (Price et al. 2017), Splash (Price 2007).

History

Citation

Astrophysical Journal, 2019, 872:163 (11pp)

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

VoR (Version of Record)

Published in

Astrophysical Journal

Publisher

American Astronomical Society, IOP Publishing

issn

0004-637X

eissn

1538-4357

Acceptance date

08/01/2019

Copyright date

2019

Available date

11/06/2019

Publisher version

https://iopscience.iop.org/article/10.3847/1538-4357/aafd2f/meta

Language

en