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Partial Stellar Disruption by a Supermassive Black Hole: Is the Light Curve Really Proportional to t(-9/4)?

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journal contribution
posted on 24.03.2020, 15:39 by Eric R Coughlin, CJ Nixon
The tidal disruption of a star by a supermassive black hole, and the subsequent accretion of the disrupted debris by that black hole, offers a direct means to study the inner regions of otherwise-quiescent galaxies. These tidal disruption events (TDEs) are being discovered at an ever-increasing rate. We present a model for the evolution of the tidally disrupted debris from a partial TDE, in which a stellar core survives the initial tidal encounter and continues to exert a gravitational influence on the expanding stream of tidally stripped debris. We use this model to show that the asymptotic fallback rate of material to the black hole in a partial TDE scales as ∝ t -2.26±0.01, and is effectively independent of the mass of the core that survives the encounter; we also estimate the rate at which TDEs approach this asymptotic scaling as a function of the core mass. These findings suggest that the late-time accretion rate onto a black hole from a TDE either declines as t -5/3 if the star is completely disrupted or t -9/4 if a core is left behind. We emphasize that previous investigations have not recovered this result due to the assumption of a Keplerian energy-period relationship for the debris orbits, which is no longer valid when a surviving core generates a time-dependent, gravitational potential. This dichotomy of fallback rates has important implications for the characteristic signatures of TDEs in the current era of wide-field surveys.

Funding

E.R.C. acknowledges support from the Lyman Spitzer Jr. Postdoctoral Fellowship, and from NASA through the Einstein Fellowship Program, grant PF6-170170, and the Hubble Fellowship, grant #HST-HF2-51433.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. C.J.N. is supported by the Science and Technology Facilities Council (grant No. ST/M005917/1).

History

Citation

Eric R. Coughlin and C. J. Nixon 2019 ApJL 883 L17

Version

VoR (Version of Record)

Published in

ASTROPHYSICAL JOURNAL LETTERS

Volume

883

Issue

1

Pagination

(6)

Publisher

IOP PUBLISHING LTD

issn

2041-8205

eissn

2041-8213

Acceptance date

03/09/2019

Copyright date

2019

Available date

23/09/2019

Publisher version

https://iopscience.iop.org/article/10.3847/2041-8213/ab412d

Language

English