The spins of supermassive black holes

2019 ◽  
Vol 15 (S356) ◽  
pp. 255-255
Author(s):  
Ranga-Ram Chary
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Circular Orbit ◽  
Supermassive Black Holes ◽  
Optical Observations ◽  
Massive Black Holes ◽  
Accretion Flow ◽  
Significant Variability ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit

AbstractWe present 1-second cadence, precise optical observations from SOFIA and Palomar of a sample of nearby supermassive black holes. The observations were taken to identify the shortest timescale variability in the nuclear photometry which may be associated with instabilities in the accretion flow in the immediate vicinity of the black hole. The shortest timescale variability, if associated with the radius of the innermost stable circular orbit (ISCO), can then be used to estimate the spin of the black hole. Despite 1% precision photometry, we obtained a non-detection of any significant variability in the nucleus of M32 (Mbh ∼ 2.5 × 106 Mȯ). Given the density of the stellar cusp, this argues for a scenario where 1000 Msun seed black holes formed from the coalescence of less massive black holes, which then accrete the gas produced by stellar interactions/winds. In more luminous systems however, we find a significant deection of variability and present hypotheses to explain the signal and thereby the origin of supermassive black holes.

scholarly journals Lyapunov exponent, ISCO and Kolmogorov–Senai entropy for Kerr–Kiselev black hole

2021 ◽  
Vol 81 (1) ◽  
Author(s):  
Monimala Mondal ◽  
Farook Rahaman ◽  
Ksh. Newton Singh
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Lyapunov Exponent ◽  
Circular Orbit ◽  
Real Root ◽  
Angular Frequency ◽  
Geodesic Motion ◽  
Radial Equation ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit

AbstractGeodesic motion has significant characteristics of space-time. We calculate the principle Lyapunov exponent (LE), which is the inverse of the instability timescale associated with this geodesics and Kolmogorov–Senai (KS) entropy for our rotating Kerr–Kiselev (KK) black hole. We have investigate the existence of stable/unstable equatorial circular orbits via LE and KS entropy for time-like and null circular geodesics. We have shown that both LE and KS entropy can be written in terms of the radial equation of innermost stable circular orbit (ISCO) for time-like circular orbit. Also, we computed the equation marginally bound circular orbit, which gives the radius (smallest real root) of marginally bound circular orbit (MBCO). We found that the null circular geodesics has larger angular frequency than time-like circular geodesics ($$Q_o > Q_{\sigma }$$ Q o > Q σ ). Thus, null-circular geodesics provides the fastest way to circulate KK black holes. Further, it is also to be noted that null circular geodesics has shortest orbital period $$(T_{photon}< T_{ISCO})$$ ( T photon < T ISCO ) among the all possible circular geodesics. Even null circular geodesics traverses fastest than any stable time-like circular geodesics other than the ISCO.

scholarly journals Reflection spectra of thick accretion discs

2019 ◽  
Vol 491 (1) ◽  
pp. 417-426 ◽  
Author(s):  
Shafqat Riaz ◽  
Dimitry Ayzenberg ◽  
Cosimo Bambi ◽  
Sourabh Nampalliwar
Keyword(s):  
Black Holes ◽  
Circular Orbit ◽  
Supermassive Black Holes ◽  
Accretion Disc ◽  
High Mass ◽  
Model Parameters ◽  
Reflection Spectra ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit ◽  
The Impact

ABSTRACT Relativistic reflection features are commonly observed in the X-ray spectra of stellar-mass and supermassive black holes and originate from illumination of the inner part of the accretion disc by a hot corona. All the available relativistic reflection models assume that the disc is infinitesimally thin and the inner edge is at the innermost stable circular orbit or at a larger radius. However, we know that several sources, especially among supermassive black holes, have quite high-mass accretion rates. In such a case, the accretion disc becomes geometrically thick and the inner edge of the disc is expected to be inside the innermost stable circular orbit. In this work, we employ the Polish donut model to describe geometrically thick discs and we study the iron-line shapes from similar systems. We also simulate full reflection spectra and we analyse the simulated observations with a thin disc relativistic reflection model to determine the impact of the disc structure on the estimation of the model parameters, in particular in the case of tests of the Kerr hypothesis.

scholarly journals Dynamics of charged and rotating NUT black holes in Rastall gravity

2020 ◽  
Vol 29 (03) ◽  
pp. 2050021
Author(s):  
Hadyan L. Prihadi ◽  
Muhammad F. A. R. Sakti ◽  
Getbogi Hikmawan ◽  
Freddy P. Zen
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Thermodynamic Properties ◽  
Circular Orbit ◽  
Black Hole Solution ◽  
Event Horizons ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit

In this work, the Kerr–Newman-NUT black hole solution in Rastall gravity is proposed and it turns out that the horizon is [Formula: see text] dependence. Black hole dynamics such as the event horizons, ergosurface, zero angular momentum observer (ZAMO), thermodynamic properties, and the equatorial circular orbit around the black hole such as static radius limit, null equatorial circular orbit, and innermost stable circular orbit are investigated in this work. How the NUT and Rastall parameter affect the dynamic of the black hole is also shown.

scholarly journals LAST ORBITS OF BINARY BLACK HOLES

2002 ◽  
Vol 17 (20) ◽  
pp. 2689-2693 ◽  
Author(s):  
ÉRIC GOURGOULHON ◽  
PHILIPPE GRANDCLÉMENT ◽  
SILVANO BONAZZOLA
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Circular Orbit ◽  
Killing Vector ◽  
Third Order ◽  
Binary Black Holes ◽  
Binary Black Hole ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit ◽  
Good Agreement

Binary black hole systems in the pre-coalescence stage are numerically constructed by demanding that the associated spacetime admits a helical Killing vector. Comparison with third order post-Newtonian calculations indicates a rather good agreement until the innermost stable circular orbit.

Black Hole Spin

2014 ◽  
Author(s):  
Charles D. Bailyn
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Accretion Disk ◽  
Circular Orbit ◽  
Kerr Black Hole ◽  
Schwarzschild Black Hole ◽  
Physical Size ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit

This chapter examines the spin of a black hole. The spin is usually described as a nondimensional parameter, which can range from zero (a nonspinning black hole) to one (a situation described as “maximally spinning”). The differences in space-time between a nonspinning Schwarzschild black hole and a Kerr black hole of the same mass have potentially observable effects. The most obvious of these differences is the position of the innermost stable circular orbit (ISCO), which has a significant effect on the inner edge of an accretion disk. It is through determination of the physical size of the ISCO that the spins of black holes are determined.

scholarly journals Circular orbits in the Taub–NUT and massless Taub–NUT spacetime

2017 ◽  
Vol 14 (07) ◽  
pp. 1750101
Author(s):  
Parthapratim Pradhan
Keyword(s):  
Black Hole ◽  
Circular Orbit ◽  
Center Of Mass ◽  
Null Geodesic ◽  
Spherically Symmetric ◽  
Potential Well ◽  
Killing Horizon ◽  
Stable Circular Orbit ◽  
Innermost Stable Circular Orbit

In this work, we study the equatorial causal geodesics of the Taub–NUT (TN) spacetime in comparison with massless TN spacetime. We emphasized both on the null circular geodesics and time-like circular geodesics. From the effective potential diagram of null and time-like geodesics, we differentiate the geodesics structure between TN spacetime and massless TN spacetime. It has been shown that there is a key role of the NUT parameter to changes the shape of pattern of the potential well in the NUT spacetime in comparison with massless NUT spacetime. We compared the innermost stable circular orbit (ISCO), marginally bound circular orbit (MBCO) and circular photon orbit (CPO) of the said spacetime with graphically in comparison with massless cases. Moreover, we compute the radius of ISCO, MBCO and CPO for extreme TN black hole (BH). Interestingly, we show that these three radii coincides with the Killing horizon, i.e. the null geodesic generators of the horizon. Finally in Appendix A, we compute the center-of-mass (CM) energy for TN BH and massless TN BH. We show that in both cases, the CM energy is finite. For extreme NUT BH, we found that the diverging nature of CM energy. First, we have observed that a non-asymptotic flat, spherically symmetric and stationary extreme BH showing such feature.

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