scholarly journals Investigation of some galactic and extragalactic gravitational phenomena

2012 ◽  
pp. 1-16 ◽  
Author(s):  
P. Jovanovic
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Accretion Disk ◽  
Supermassive Black Holes ◽  
Bright Spot ◽  
Kerr Metric ◽  
Massive Black Hole ◽  
Spacetime Geometry ◽  
Supermassive Black Hole

Here we present a short overview of the most important results of our investigations of the following galactic and extragalactic gravitational phenomena: supermassive black holes in centers of galaxies and quasars, supermassive black hole binaries, gravitational lenses and dark matter. For the purpose of these investigations, we developed a model of a relativistic accretion disk around a supermassive black hole, based on the ray-tracing method in the Kerr metric, a model of a bright spot in an accretion disk and three different models of gravitational microlenses. All these models enabled us to study physics, spacetime geometry and effects of strong gravity in the vicinity of supermassive black holes, variability of some active galaxies and quasars, different effects in the lensed quasars with multiple images, as well as the dark matter fraction in the Universe. We also found an observational evidence for the first spectroscopically resolved sub-parsec orbit of a supermassive black hole binary system in the core of active galaxy NGC 4151. Besides, we studied applications of one potential alternative to dark matter in the form of a modified theory of gravity on Galactic scales, to explain the recently observed orbital precession of some S-stars, which are orbiting around a massive black hole at the Galactic center.

Determination of supermassive black hole spins in active galactic nuclei

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040054
Author(s):  
M. Yu. Piotrovich ◽  
V. L. Afanasiev ◽  
S. D. Buliga ◽  
T. M. Natsvlishvili
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Disk Model ◽  
Supermassive Black Hole

Based on spectropolarimetry for a number of active galactic nuclei in Seyfert 1 type galaxies observed with the 6-m BTA telescope, we have estimated the spins of the supermassive black holes at the centers of these galaxies. We have determined the spins based on the standard Shakura-Sunyaev accretion disk model. More than 70% of the investigated active galactic nuclei are shown to have Kerr supermassive black holes with a dimensionless spin greater than 0.9.

scholarly journals The ecology of the galactic centre: Nuclear stellar clusters and supermassive black holes

2019 ◽  
Vol 14 (S351) ◽  
pp. 80-83 ◽  
Author(s):  
Melvyn B. Davies ◽  
Abbas Askar ◽  
Ross P. Church
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Large Fraction ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Galactic Centre ◽  
Stellar Clusters ◽  
Stellar Cluster ◽  
Supermassive Black Hole ◽  
Multiple Clusters

AbstractSupermassive black holes are found in most galactic nuclei. A large fraction of these nuclei also contain a nuclear stellar cluster surrounding the black hole. Here we consider the idea that the nuclear stellar cluster formed first and that the supermassive black hole grew later. In particular we consider the merger of three stellar clusters to form a nuclear stellar cluster, where some of these clusters contain a single intermediate-mass black hole (IMBH). In the cases where multiple clusters contain IMBHs, we discuss whether the black holes are likely to merge and whether such mergers are likely to result in the ejection of the merged black hole from the nuclear stellar cluster. In some cases, no supermassive black hole will form as any merger product is not retained. This is a natural pathway to explain those galactic nuclei that contain a nuclear stellar cluster but apparently lack a supermassive black hole; M33 being a nearby example. Alternatively, if an IMBH merger product is retained within the nuclear stellar cluster, it may subsequently grow, e.g. via the tidal disruption of stars, to form a supermassive black hole.

scholarly journals Supermassive black holes surrounded by dark matter modeled as anisotropic fluid: epicyclic oscillations and their fitting to observed QPOs

2021 ◽  
Vol 2021 (11) ◽  
pp. 059
Author(s):  
Z. Stuchlík ◽  
J. Vrba
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Anisotropic Fluid ◽  
Physical Parameters ◽  
Black Hole Spacetimes ◽  
Test Particles

Abstract Recently introduced exact solution of the Einstein gravity coupled minimally to an anisotropic fluid representing dark matter can well represent supermassive black holes in galactic nuclei with realistic distribution of dark matter around the black hole, given by the Hernquist-like density distribution. For these fluid-hairy black hole spacetimes, properties of the gravitational radiation, quasinormal ringing, and optical phenomena were studied, giving interesting results. Here, using the range of physical parameters of these spacetimes allowing for their relevance in astrophysics, we study the epicyclic oscillatory motion of test particles in these spacetimes. The frequencies of the orbital and epicyclic motion are applied in the epicyclic resonance variant of the geodesic model of quasiperiodic oscillations (QPOs) observed in active galactic nuclei to demonstrate the possibility to solve the cases where the standard vacuum black hole spacetimes are not allowing for explanation of the observed data. We demonstrate that the geodesic model can explain the QPOs observed in most of the active galactic nuclei for the fluid-hairy black holes with reasonable halo parameters.

scholarly journals The Role of Gravitational Instabilities in the Feeding of Supermassive Black Holes

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
Giuseppe Lodato
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
High Redshift ◽  
Supermassive Black Holes ◽  
Point Of View ◽  
Accretion Discs ◽  
Theoretical Point ◽  
Interstellar Gas ◽  
Massive Black Hole

I review the recent progresses that have been obtained, especially through the use of high-resolution numerical simulations, on the dynamics of self-gravitating accretion discs. A coherent picture is emerging, where the disc dynamics is controlled by a small number of parameters that determine whether the disc is stable or unstable, whether the instability saturates in a self-regulated state or runs away into fragmentation, and whether the dynamics is local or global. I then apply these concepts to the case of AGN discs, discussing the implications of such evolution on the feeding of supermassive black holes. Nonfragmenting, self-gravitating discs appear to play a fundamental role in the process of formation of massive black hole seeds at high redshift ( 10–15) through direct gas collapse. On the other hand, the different cooling properties of the interstellar gas at low redshifts determine a radically different behaviour for the outskirts of the accretion discs feeding typical AGNs. Here the situation is much less clear from a theoretical point of view, and while several observational clues point to the important role of massive discs at a distance of roughly a parsec from their central black hole, their dynamics is still under debate.

Primordial black holes and the observable features of the universe

2015 ◽  
Vol 24 (13) ◽  
pp. 1545005 ◽  
Author(s):  
K. M. Belotsky ◽  
A. A. Kirillov ◽  
S. G. Rubin
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Galactic Center ◽  
Mass Range ◽  
Primordial Black Holes ◽  
Simultaneous Solution ◽  
Supermassive Black Hole ◽  
Range Distribution ◽  
The Universe

Here, we briefly discuss the possibility to solve simultaneously with primordial black holes (PBHs) the problems of dark matter (DM), reionization of the universe, origin of positron line from Galactic center and supermassive black hole (BH) in it. Discussed scenario can naturally lead to a multiple-peak broad-mass-range distribution of PBHs in mass, which is necessary for simultaneous solution of the problems.

scholarly journals Dormant Black Holes

2017 ◽  
Vol 45 ◽  
pp. 1760022
Author(s):  
José Antonio de Freitas Pacheco
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Accretion Disk ◽  
Supermassive Black Holes ◽  
Host Galaxy ◽  
Nuclear Activity ◽  
Dormant State

The growth of supermassive black holes is intermittent, having periods of low accretion when no nuclear activity is seen in the center of the host galaxy. In such dormant state black holes may tidally disrupt stars scattered from the bulge to inside their influence sphere. The resulting debris are partially captured by the black hole forming a short-lived accretion disk, which produces a variable emission dubbed “tidal flare”. Some galaxies candidate to have hosted these tidal events are here considered.

scholarly journals Axion core–halo mass and the black hole–halo mass relation: constraints on a few parsec scales

2019 ◽  
Vol 488 (4) ◽  
pp. 4497-4503 ◽  
Author(s):  
Vincent Desjacques ◽  
Adi Nusser
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Numerical Simulations ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Mass Relation ◽  
Axion Mass

ABSTRACT If the dark matter is made of ultralight axions, stable solitonic cores form at the centres of virialized haloes. In some range for the mass m of the axion particle, these cores are sufficiently compact and can mimic supermassive black holes (SMBH) residing at galactic nuclei. We use the solitonic core–halo mass relation, validated in numerical simulations, to constrain a new range of allowed axion mass from measurements of the SMBH mass in (pseudo)bulge and bulgeless galaxies. These limits are based on observations of galactic nuclei on scales smaller than 10 pc. Our analysis suggests that $m\lesssim 10^{-18}\, {\rm eV}$ is ruled out by the data. We briefly discuss whether an attractive self-interaction among axions could alleviate this constraint.

Formation history of supermassive black holes in a viable cosmological window

2006 ◽  
Vol 2 (S238) ◽  
pp. 345-346
Author(s):  
Carlos H. Coimbra-Araújo ◽  
Amâncio C. S. Friaça
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Supermassive Black Holes ◽  
Intermediate Mass ◽  
Disk Model ◽  
Rapid Rotation ◽  
Supermassive Black Hole ◽  
Formation History ◽  
History Of ◽  
Stable Part

AbstractWe show, performing a viable cosmological window, that only the magneto hydrodynamic (MHD) disk model is capable to explain how an intermediate mass black hole (IMBH) (with masses ∼ 103M⊙) grows unto a supermassive black hole (SMBH) (with masses ∼ 107M⊙). We still calculate the supermassive stars sequence of stability. Those stars, with synthetized helium or oxygen cores, collapse to form IMBHs. In our calculation we show that the primordial stars must have rapid rotation if they are in the stable part of the sequence.

scholarly journals A fast and long-lived outflow from the supermassive black hole in NGC 5548

Science ◽  
2014 ◽  
Vol 345 (6192) ◽  
pp. 64-68 ◽  
Author(s):  
J. S. Kaastra ◽  
G. A. Kriss ◽  
M. Cappi ◽  
M. Mehdipour ◽  
P.-O. Petrucci ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
High Resolution ◽  
Accretion Disk ◽  
Active Galaxies ◽  
Ionized Gas ◽  
X Ray ◽  
Supermassive Black Hole ◽  
Space Observatories ◽  
Ngc 5548

Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and high-resolution x-ray and ultraviolet (UV) observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas not seen before. It blocks 90% of the soft x-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and, at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.

scholarly journals Accretion disc luminosity for black holes surrounded by dark matter

2020 ◽  
Vol 496 (2) ◽  
pp. 1115-1123
Author(s):  
K Boshkayev ◽  
A Idrissov ◽  
O Luongo ◽  
D Malafarina
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Refractive Index ◽  
Dark Matter ◽  
Early Universe ◽  
Space Time ◽  
Supermassive Black Holes ◽  
Accretion Disc ◽  
Mass Estimation ◽  
Static Black Hole

ABSTRACT We consider the observational properties of a static black hole space–time immersed in a dark matter envelope. We investigate how the modifications to geometry induced by the presence of dark matter affect the luminosity of the black hole’s accretion disc. We show that the same disc luminosity as produced by a black hole in vacuum may be produced by a smaller black hole surrounded by dark matter under certain conditions. In particular, we demonstrate that the luminosity of the disc is markedly altered by the presence of dark matter, suggesting that the mass estimation of distant supermassive black holes may be changed if they are immersed in dark matter. We argue that a similar effect holds in more realistic scenarios, and we discuss the refractive index related to dark matter lensing. Finally, we show how the results presented here may help to explain the observed luminosity of supermassive black holes in the early Universe.

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