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Abstract Close encounters between stellar-mass black holes (BHs) and stars occur frequently in dense star clusters and in the disks of active galactic nuclei. Recent studies have shown that in highly eccentric close encounters, the star can be tidally disrupted by the BH in a microtidal disruption event (microTDE), resulting in rapid mass accretion and possibly bright electromagnetic signatures. Here we consider a scenario in which the star might approach the stellar-mass BH in a gradual, nearly circular inspiral, under the influence of dynamical friction in a circum-binary gas disk or three-body interactions in a star cluster. We perform hydrodynamics simulations of this scenario using the smoothed particle hydrodynamics codePHANTOM. We find that under certain circumstances (for initial eccentricitye0≳ 0.4 and penetration factorβ= 1, ore0< 0.4 andβ≲ 0.67), the mass of the star is slowly stripped away by the BH. We call this gradual tidal disruption a “tidal-peeling event.” Additionally, we discover that some low-eccentricity microTDEs (e0< 0.4 andβ= 1) are a new form of fast luminous transients similar to parabolic microTDEs. Depending on the initial distance and eccentricity of the encounter, these low-eccentricity microTDEs might exhibit significant accretion rates and orbital evolution distinct from those of a typical (eccentric) microTDE.
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Partial tidal disruption events by stellar mass black holes: Gravitational instability of stream and impact from remnant core
ABSTRACT In dense star clusters, such as globular and open clusters, dynamical interactions between stars and black holes (BHs) can be extremely frequent, leading to various astrophysical transients. Close encounters between a star and a stellar mass BH make it possible for the star to be tidally disrupted by the BH. Due to the relative low mass of the BH and the small cross-section of the tidal disruption event (TDE) for cases with high penetration, disruptions caused by close encounters are usually partial disruptions. The existence of the remnant stellar core and its non-negligible mass compared to the stellar mass BH alters the accretion process significantly. We study this problem with SPH simulations using the code Phantom, with the inclusion of radiation pressure, which is important for small mass BHs. Additionally, we develop a new, more general method of computing the fallback rate which does not rely on any approximation. Our study shows that the powerlaw slope of the fallback rate has a strong dependence on the mass of the BH in the stellar mass BH regime. Furthermore, in this regime, self-gravity of the fallback stream and local instabilities become more significant, and cause the disrupted material to collapse into small clumps before returning to the BH. This results in an abrupt increase of the fallback rate, which can significantly deviate from a powerlaw. Our results will help in the identification of TDEs by stellar mass BHs in dense clusters.
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- Award ID(s):
- 2006839
- PAR ID:
- 10249423
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 503
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 6005 to 6015
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/stab802
