All ten LIGO/Virgo binary black hole (BHBH) coalescences reported following the O1/O2 runs have nearzero effective spins. There are only three potential explanations for this. If the BH spin magnitudes are large, then: (i) either both BH spin vectors must be nearly in the orbital plane or (ii) the spin angular momenta of the BHs must be oppositely directed and similar in magnitude. Then there is also the possibility that (iii) the BH spin magnitudes are small. We consider the third hypothesis within the framework of the classical isolated binary evolution scenario of the BHBH merger formation. We test threemore »
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 crosssection 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 nonnegligible 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, selfgravity of the fallback stream and local instabilities become more significant, and cause the disrupted material to collapse into more »
 Award ID(s):
 2006839
 Publication Date:
 NSFPAR ID:
 10249423
 Journal Name:
 Monthly Notices of the Royal Astronomical Society
 Volume:
 503
 Issue:
 4
 Page Range or eLocationID:
 6005 to 6015
 ISSN:
 00358711
 Sponsoring Org:
 National Science Foundation
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