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.

scholarly journals Gravitating Disks Around Black Holes

2009 ◽  
Vol 5 (S267) ◽  
pp. 332-332
Author(s):  
Vladimír Karas ◽  
Ladislav Šubr
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Relativistic Effects ◽  
Einstein Equations ◽  
Axially Symmetric ◽  
Disk System ◽  
Massive Black Hole ◽  
Black Hole Binary

AbstractFluid disks and tori around black holes are discussed within different approaches and with the emphasis on the role of disk gravity. We first review the prospects for investigating the gravitational field of a black hole–disk system by analytical solutions of stationary, axially symmetric Einstein equations. More detailed considerations are focused on the middle and outer parts of extended disk-like configurations where relativistic effects are small and the Newtonian description is adequate. As an example, we investigate the case of a torus near a massive black hole that is a member of the black-hole binary system.

scholarly journals The role of relativistic jets in the heaviest and most active supermassive black holes at high redshift

2013 ◽  
Vol 432 (4) ◽  
pp. 2818-2823 ◽  
Author(s):  
G. Ghisellini ◽  
F. Haardt ◽  
R. Della Ceca ◽  
M. Volonteri ◽  
T. Sbarrato
Keyword(s):  
Black Holes ◽  
High Redshift ◽  
Supermassive Black Holes ◽  
Relativistic Jets

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.

scholarly journals Observational Evidence for Supermassive Black Holes

1989 ◽  
Vol 134 ◽  
pp. 217-232
Author(s):  
Alan Dressler
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Hubble Space Telescope ◽  
Stellar Dynamics ◽  
Supermassive Black Holes ◽  
Massive Black Hole ◽  
Central Mass ◽  
Nearby Galaxies ◽  
Straightforward Interpretation ◽  
Rule Out

A growing body of evidence from stellar dynamics in the nuclei of galaxies indicates that supermassive black holes of 107–109 M0 are common. The two best cases are M31 and M32, for which dark, central mass concentrations are the only straightforward interpretation. M87 continues to be a possible location of an even more massive black hole, but new observations and models by the author and D. Richstone effectively rule out the high black hole mass ∼5 × 109 M0 claimed by Sargent, Young, and collaborators. New data are available for several other nearby galaxies which also show kinematic signatures that could also be due to supermassive black holes. The Hubble Space Telescope will play the key role in strengthening these cases and eliminating, for the best examples, alternative models which do not require supermassive black holes.

scholarly journals Verbena officinalis Verbenaceae (Lamiales): a new plant model system for phyllotaxis research

2021 ◽  
Author(s):  
Beata Zagórska-Marek ◽  
Magdalena Turzańska ◽  
Klaudia Chmiel
Keyword(s):  
Vascular System ◽  
Cumulative Effect ◽  
Point Of View ◽  
Theoretical Point ◽  
Inflorescence Axis ◽  
Organ Identity ◽  
Lateral Organ ◽  
Complex Relationships ◽  
Secondary Transitions

AbstractPhyllotactic diversity and developmental transitions between phyllotactic patterns are not fully understood. The plants studied so far, such as Magnolia, Torreya or Abies, are not suitable for experimental work, and the most popular model plant, Arabidopsis thaliana, does not show sufficient phyllotactic variability. It has been found that in common verbena (Verbena officinalis L.), a perennial, cosmopolitan plant, phyllotaxis differs not only between growth phases in primary transitions but also along the indeterminate inflorescence axis in a series of multiple secondary transitions. The latter are no longer associated with the change in lateral organ identity, and the sequence of phyllotactic patterns is puzzling from a theoretical point of view. Data from the experiments in silico, confronted with empirical observations, suggest that secondary transitions might be triggered by the cumulative effect of fluctuations in the continuously decreasing bract primordia size. The most important finding is that the changes in the primary vascular system, associated with phyllotactic transitions, precede those taking place at the apical meristem. This raises the question of the role of the vascular system in determining primordia initiation sites, and possibly challenges the autonomy of the apex. The results of this study highlight the complex relationships between various systems that have to coordinate their growth and differentiation in the developing plant shoot. Common verbena emerges from this research as a plant that may become a new model suitable for further studies on the causes of phyllotactic transitions.

scholarly journals Epicyclic Oscillations around Simpson–Visser Regular Black Holes and Wormholes

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 279
Author(s):  
Zdeněk Stuchlík ◽  
Jaroslav Vrba
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Active Galactic Nuclei ◽  
Observational Data ◽  
High Frequency ◽  
Galactic Nuclei ◽  
Supermassive Black Holes ◽  
Periodic Oscillations ◽  
High Length ◽  
Circular Geodesic

We study epicyclic oscillatory motion along circular geodesics of the Simpson–Visser meta-geometry describing in a unique way regular black-bounce black holes and reflection-symmetric wormholes by using a length parameter l. We give the frequencies of the orbital and epicyclic motion in a Keplerian disc with inner edge at the innermost circular geodesic located above the black hole outer horizon or on the our side of the wormhole. We use these frequencies in the epicyclic resonance version of the so-called geodesic models of high-frequency quasi-periodic oscillations (HF QPOs) observed in microquasars and around supermassive black holes in active galactic nuclei to test the ability of this meta-geometry to improve the fitting of HF QPOs observational data from the surrounding of supermassive black holes. We demonstrate that this is really possible for wormholes with sufficiently high length parameter l.

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 The female characters in Branislav Nušić's and Stefan Kostov's selected comedies

Bastina ◽  
2020 ◽  
pp. 95-109
Author(s):  
Đurđina Isić
Keyword(s):  
Small Town ◽  
Point Of View ◽  
Theoretical Point ◽  
Female Characters ◽  
Modern Age ◽  
The Social ◽  
The World ◽  
The Subject ◽  
Bereaved Family

The paper presents the results of research that included comparative study of the place and role of female characters in selected and representative comedies by Serbian comedigrapher Branislav Nušić (eng. MP, Suspicious person, Mrs Minister, Bereaved family, Dr, Deceased; srb. Narodni poslanik, Sumnjivo lice, Ožalošćena porodica, Dr, Pokojnik, Vlast) and Bulgarian comedigrapher Stefan Kostov (eng. Gold mine, Golemanov, Grasshoppers, Nameless comedy; blg. Zlamnama mina, Golemanov, Skakalci, Komediâ bez ime) in order to find similarities and differences in the process of comedigraphic shaping of female characters in the work of these two authors. The subject of the research was viewed primarily from a literary-theoretical point of view, and the dominant methods of study were comparative and analytical-synthetic. During the research, there was a differentiation of female characters in accordance with their motivational structures, psychological assemblies and the nature of the place and the role they play in the social environment in which they are located. Therefore, we can distinguish female characters who live in the province and who are fully representative of the small-town spirit, female characters who live in the capital and are a symbol of the modern age and female characters who dwell in the capital, but in fact, deeply down still carry a small-town view of the world. The structure of this paper is in line with this distinction. Conclusions made at the end of the study show that the representation of female characters in analyzed comedies of both comedigaphers is highly similar in its nature.

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.

The Role of Business Schools in Marketing Education

2021 ◽  
pp. 42-56
Author(s):  
Andre Vilares Morgado
Keyword(s):  
Business Schools ◽  
Marketing Research ◽  
Point Of View ◽  
Theory And Practice ◽  
Theoretical Point ◽  
Marketing Theory ◽  
Marketing Education ◽  
Inductive Approach

Business schools play a key role in training marketing professionals. However, there is a strong divide between the expectations held by marketing professionals and those held in academia. This article considers this phenomenon from a theoretical point of view and explores its causes. The author argues that business schools are able to play a key role in bridging theory and practice in marketing. The article closes by offering several suggestions for how business schools might increase the relevance of marketing research while reducing the gap between marketing theory and practice. In particular, the article suggests the adoption of an inductive approach to research and offers a set of policies that business schools can implement in order to close this gap.

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