Tidal Disruptions of Main-sequence Stars. IV. Relativistic Effects and Dependence on Black Hole Mass

ABSTRACT Using general relativistic magnetohydrodynamic simulations of accreting black holes, we show that a suitable subtraction of the linear polarization per pixel from total intensity images can enhance the photon ring feature. We find that the photon ring is typically a factor of ≃2 less polarized than the rest of the image. This is due to a combination of plasma and general relativistic effects, as well as magnetic turbulence. When there are no other persistently depolarized image features, adding the subtracted residuals over time results in a sharp image of the photon ring. We show that the method works well for sample, viable GRMHD models of Sgr A* and M87*, where measurements of the photon ring properties would provide new measurements of black hole mass and spin, and potentially allow for tests of the ‘no-hair’ theorem of general relativity.

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Tidal disruption events on to stellar black holes in triples

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2213 ◽

2019 ◽

Vol 489 (1) ◽

pp. 727-737 ◽

Cited By ~ 8

Author(s):

Giacomo Fragione ◽

Nathan W C Leigh ◽

Rosalba Perna ◽

Bence Kocsis

Keyword(s):

Black Holes ◽

Black Hole ◽

Gravitational Force ◽

Main Sequence ◽

Initial Conditions ◽

Main Sequence Stars ◽

Tidal Disruption ◽

Mean Velocity ◽

Massive Black Holes ◽

The Mean

ABSTRACT Stars passing too close to a black hole can produce tidal disruption events (TDEs), when the tidal force across the star exceeds the gravitational force that binds it. TDEs have usually been discussed in relation to massive black holes that reside in the centres of galaxies or lurk in star clusters. We investigate the possibility that triple stars hosting a stellar black hole (SBH) may be sources of TDEs. We start from a triple system made up of three main-sequence stars and model the supernova (SN) kick event that led to the production of an inner binary comprised of an SBH. We evolve these triples with a high-precision N-body code and study their TDEs as a result of Kozai–Lidov oscillations. We explore a variety of distributions of natal kicks imparted during the SN event, various maximum initial separations for the triples, and different distributions of eccentricities. We show that the main parameter that governs the properties of the SBH–MS binaries that produce a TDE in triples is the mean velocity of the natal kick distribution. Smaller σ’s lead to larger inner and outer semimajor axes of the systems that undergo a TDE, smaller SBH masses, and longer time-scales. We find that the fraction of systems that produce a TDE is roughly independent of the initial conditions, while estimate a TDE rate of $2.1\times 10^{-4}{\!-\!}4.7 \, \mathrm{yr}^{-1}$, depending on the prescriptions for the SBH natal kicks. This rate is almost comparable to the expected TDE rate for massive black holes.

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The capture of main sequence stars and giant stars by a massive black hole

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307005662 ◽

2006 ◽

Vol 2 (S238) ◽

pp. 403-404

Author(s):

Y. Lu ◽

Y. F Huang ◽

Z. Zheng ◽

S. N. Zhang

Keyword(s):

Black Hole ◽

Gamma Rays ◽

Main Sequence ◽

Gamma Ray ◽

High Energy ◽

Main Sequence Stars ◽

Massive Black Hole ◽

Giant Stars ◽

Very High Energy ◽

Very High

AbstractSince the mass-radius relation is quite different for a main sequence (MS) star and a giant (G) star, we find that the radiation efficiencies in the star capture processes by a black hole (BH) are also very different. This may provide a useful way to distinguish the capture of MS and G stars. Comparing with observations of the very high energy (VHE) gamma-ray emissions, we argue the event that triggers the gamma-ray emission in the energy range 4–40 TeV should be a G star capture. On the other hand, the capture of MS stars by the massive BH is required when the measured spectrum of VHE gamma-rays extends from 109 to 1015 eV.

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Comment on “A noninteracting low-mass black hole–giant star binary system”

Science ◽

10.1126/science.aba3282 ◽

2020 ◽

Vol 368 (6491) ◽

pp. eaba3282 ◽

Cited By ~ 7

Author(s):

Ed P. J. van den Heuvel ◽

Thomas M. Tauris

Keyword(s):

Black Hole ◽

Main Sequence ◽

Close Binary ◽

Main Sequence Stars ◽

Solar Mass ◽

Giant Star ◽

X Ray ◽

Low Mass ◽

Red Giant ◽

Star Binary

Thompson et al. (Reports, 1 November 2019, p. 637) interpreted the unseen companion of the red giant star 2MASS J05215658+4359220 as most likely a black hole. We argue that if the red giant’s mass is ~1 solar mass, its companion can be a close binary consisting of two main-sequence stars. This would explain why no x-ray emission is detected from the system.

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The thermodynamics of collapsars

10.20944/preprints201607.0058.v1 ◽

2016 ◽

Author(s):

Trevor W. Marshall

Keyword(s):

Black Holes ◽

Black Hole ◽

Neutron Stars ◽

Main Sequence ◽

Main Sequence Stars ◽

Field Equations ◽

Gravitational Radius ◽

Final Density ◽

Shell Models ◽

Independent Case

This article argues that there is a consistent description of gravitationally collapsed bodies, including neutron stars above the Tolman-Oppenheimer-Volkoff mass and also supermassive galactic centres, according to which collapse stops before the object reaches its gravitational radius, the density reaching a maximum close to the surface and then decreasing towards the centre. Models for such shell-like objects have been constructed using classic formulations found in the 1939 articles of Oppenheimer-Volkoff and Oppenheimer-Snyder. It was possible to modify the conclusions of the first article by changing the authors’ boundary conditions at r = 0. In the second case we find that the authors’ solution of the field equations needs no changes, but that the choice of their article’s title led many of their successors to believe that it supports the black-hole hypothesis. However, it is easily demonstrated that their final density distribution accords with the shell models found in our articles. Because black holes, according to many formulations, "have no hair", their thermodynamics is rather simple. The kind of collapsar which our models describe are more like main-sequence stars; they have spatiotemporal distributions of pressure, density and temperature, that is they have hair. In this article we shall concentrate on the dynamics of the Oppenheimer-Snyder collapsar; both pressure and temperature are everywhere zero, so there can be no thermodynamics. Only in the time independent case of Oppenheimer-Volkoff type models is it currently feasible to consider some thermodynamic implications; here some valuable new insights are obtained through the incorporation of the Oppenheimer-Snyder dynamics.

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The methods for searching hypervelocity star candidates from the SDSS

Proceedings of the International Astronomical Union ◽

10.1017/s174392131300687x ◽

2013 ◽

Vol 9 (S298) ◽

pp. 421-421

Author(s):

Yinbi Li ◽

Ali Luo ◽

Gang Zhao ◽

Youjun Lu

Keyword(s):

Black Hole ◽

Velocity Distribution ◽

Radial Velocity ◽

Binary Stars ◽

High Velocity ◽

Main Sequence ◽

Galactic Center ◽

Main Sequence Stars ◽

Massive Black Hole ◽

Stellar Spectra

AbstractHyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions of (binary) stars with the central massive black hole(s). In this paper, we firstly select F and G type main sequence stars from about 370,000 stellar spectra of DR7. Then, we select 369 high velocity stars from main sequence samples using the radial velocity distribution. Finally, we find 13 possible unbound hyper-velocity star candidates from the 369 high velocity stars.

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Gravitational waves from bodies orbiting the Galactic center black hole and their detectability by LISA

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935406 ◽

2019 ◽

Vol 627 ◽

pp. A92 ◽

Cited By ~ 7

Author(s):

E. Gourgoulhon ◽

A. Le Tiec ◽

F. H. Vincent ◽

N. Warburton

Keyword(s):

Black Holes ◽

Black Hole ◽

Main Sequence ◽

Signal To Noise Ratio ◽

Brown Dwarfs ◽

Compact Objects ◽

Main Sequence Stars ◽

Signal To Noise ◽

Noise Ratio ◽

Sgr A

Aims. We present the first fully relativistic study of gravitational radiation from bodies in circular equatorial orbits around the massive black hole at the Galactic center, Sgr A* and we assess the detectability of various kinds of objects by the gravitational wave detector LISA. Methods. Our computations are based on the theory of perturbations of the Kerr spacetime and take into account the Roche limit induced by tidal forces in the Kerr metric. The signal-to-noise ratio in the LISA detector, as well as the time spent in LISA band, are evaluated. We have implemented all the computational tools in an open-source SageMath package, within the Black Hole Perturbation Toolkit framework. Results. We find that white dwarfs, neutrons stars, stellar black holes, primordial black holes of mass larger than 10−4 M⊙, main-sequence stars of mass lower than ∼2.5 M⊙, and brown dwarfs orbiting Sgr A* are all detectable in one year of LISA data with a signal-to-noise ratio above 10 for at least 105 years in the slow inspiral towards either the innermost stable circular orbit (compact objects) or the Roche limit (main-sequence stars and brown dwarfs). The longest times in-band, of the order of 106 years, are achieved for primordial black holes of mass ∼10−3 M⊙ down to 10−5 M⊙, depending on the spin of Sgr A*, as well as for brown dwarfs, just followed by white dwarfs and low mass main-sequence stars. The long time in-band of these objects makes Sgr A* a valuable target for LISA. We also consider bodies on close circular orbits around the massive black hole in the nucleus of the nearby galaxy M 32 and find that, among them, compact objects and brown dwarfs stay for 103–104 years in LISA band with a one-year signal-to-noise ratio above ten.

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