8. Black holes and spin-offs

2015 ◽  
Author(s):  
Katherine Blundell
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Particle Acceleration ◽  
Synchrotron Radiation ◽  
Shock Waves ◽  
Event Horizon ◽  
Intergalactic Medium ◽  
Active Galaxies ◽  
Shock Region

Black holes influence and interact with their surroundings. Plasma lobes exhibited by some active galaxies are created by jets that are squirted out from the immediate surroundings of a black hole, outside the event horizon. When the jets impinge on the intergalactic medium, shock waves form within which spectacular particle acceleration occurs, and the energized plasma which originated from near the black hole, billows up and flows out of the immediate shock region. As the plasma expands, it imparts enormous quantities of energy to the intergalactic medium. ‘Black holes and spin-offs’ describes the powerful luminosity of quasars, their synchrotron radiation, and the much smaller microquasars.

scholarly journals LUKEWARM BLACK HOLES IN QUADRATIC GRAVITY

2011 ◽  
Vol 26 (14) ◽  
pp. 999-1007 ◽  
Author(s):  
JERZY MATYJASEK ◽  
KATARZYNA ZWIERZCHOWSKA
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Fourth Order ◽  
Spherically Symmetric ◽  
Cosmological Horizon ◽  
De Sitter ◽  
Quadratic Gravity ◽  
De Sitter Universe ◽  
Electrically Charged

Perturbative solutions to the fourth-order gravity describing spherically-symmetric, static and electrically charged black hole in an asymptotically de Sitter universe is constructed and discussed. Special emphasis is put on the lukewarm configurations, in which the temperature of the event horizon equals the temperature of the cosmological horizon.

3. Extrasolar tests of gravity

2017 ◽  
pp. 35-45
Author(s):  
Timothy Clifton
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Solar System ◽  
Neutron Stars ◽  
Event Horizon ◽  
Gravitational Fields ◽  
Binary Pulsars ◽  
Tests Of Gravity ◽  
Triple Star

By studying objects outside our Solar System, we can observe star systems with far greater gravitational fields. ‘Extrasolar tests of gravity’ considers stars of different sizes that have undergone gravitational collapse, including white dwarfs, neutron stars, and black holes. A black hole consists of a region of space-time enclosed by a surface called an event horizon. The gravitational field of a black hole is so strong that anything that finds its way inside the event horizon can never escape. Other star systems considered are binary pulsars and triple star systems. With the invention of even more powerful telescopes, there will be more tantalizing possibilities for testing gravity in the future.

Entropy bound of horizons of some regular black holes

2020 ◽  
Vol 35 (10) ◽  
pp. 2050070
Author(s):  
Ujjal Debnath
Keyword(s):  
Black Holes ◽  
Heat Capacity ◽  
Black Hole ◽  
Specific Heat ◽  
Surface Area ◽  
Event Horizon ◽  
Specific Heat Capacity ◽  
Thermodynamic Quantities ◽  
Event Horizons ◽  
Regular Black Hole

We study the four-dimensional (i) modified Bardeen black hole, (ii) modified Hayward black hole, (iii) charged regular black hole and (iv) magnetically charged regular black hole. For modified Bardeen black hole and modified Hayward black hole, we found only one horizon (event horizon) and then we found some thermodynamic quantities like the entropy, surface area, irreducible mass, temperature, Komar energy and specific heat capacity on the event horizon. We here study the bounds of the above thermodynamic quantities for these black holes on the event horizon. Then, we examine the thermodynamics stability of the black holes with some conditions. Next, we studied the charged regular black hole and magnetically charged regular black hole and found two horizons (Cauchy and event horizons) of these black holes. Then, we found the entropy, surface area, irreducible mass, temperature, Komar energy and specific heat capacity on the Cauchy and event horizons. Then, we get some conditions for thermodynamic stability/instability of the black holes. We found the radius of the extremal horizon and Christodoulou–Ruffiini mass and then analyze the above thermodynamic quantities on the extremal horizon. We calculate the sum/subtraction, product, division and sum/subtraction of inverse of surface areas, entropies, irreducible masses, temperatures, Komar energies and specific heat capacities on both the horizons. From these, we found the bounds of the above quantities on the horizons.

More on extracting information about the initial state from the black hole radiation

2018 ◽  
Vol 33 (19) ◽  
pp. 1850108
Author(s):  
Hossein Ghaforyan ◽  
Somayyeh Shoorvazi ◽  
Alireza Sepehri ◽  
Tooraj Ghaffary
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Density Matrix ◽  
Quantum Entanglement ◽  
Event Horizon ◽  
Initial State ◽  
Black Hole Radiation ◽  
Total Information ◽  
Quantum Treatment ◽  
Collapse Process

Recently, some authors showed that a classical collapse scenario ignores this richness of information in the resulting spectrum and a consistent quantum treatment of the entire collapse process might allow us to retrieve much more information from the spectrum of the final radiation. We confirm these results and show that by considering the quantum entanglement between metrics, we can uncover information of black holes. In our model, a density matrix is defined for the spaces, both inside and outside of the event horizon. These inside and outside spaces of black holes are obtained by tracing from a bigger space. An observer that lives in this big space can recover total information regarding the inside and outside of black hole.

2. Navigating through spacetime

2015 ◽  
Author(s):  
Katherine Blundell
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Light Cone ◽  
Mathematical Language ◽  
Theory Of Relativity ◽  
Left Behind ◽  
Physical Universe

Mathematics is the perfect language needed for describing how the theory of relativity applies to the physical Universe and all of spacetime, and that description includes the strange behaviour that occurs near black holes. ‘Navigating through spacetime’ explains some of the complicated mathematical language using spacetime diagrams. It describes world-lines—the path left behind as an object journeys through spacetime—and light cones. Black holes profoundly affect the orientations of the light cones. As a particle approaches a black hole, its future light cone tilts more and more towards the black hole. When the particle crosses the event horizon, all of its possible future trajectories end inside the black hole.

scholarly journals Gas filaments of the cosmic web located around active galaxies in a protocluster

Science ◽  
2019 ◽  
Vol 366 (6461) ◽  
pp. 97-100 ◽  
Author(s):  
H. Umehata ◽  
M. Fumagalli ◽  
I. Smail ◽  
Y. Matsuda ◽  
A. M. Swinbank ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Star Formation ◽  
Ionizing Radiation ◽  
Rest Frame ◽  
Active Galaxies ◽  
Intergalactic Gas ◽  
Supermassive Black Hole ◽  
The Universe ◽  
Intense Star Formation

Cosmological simulations predict that the Universe contains a network of intergalactic gas filaments, within which galaxies form and evolve. However, the faintness of any emission from these filaments has limited tests of this prediction. We report the detection of rest-frame ultraviolet Lyman-α radiation from multiple filaments extending more than one megaparsec between galaxies within the SSA22 protocluster at a redshift of 3.1. Intense star formation and supermassive black-hole activity is occurring within the galaxies embedded in these structures, which are the likely sources of the elevated ionizing radiation powering the observed Lyman-α emission. Our observations map the gas in filamentary structures of the type thought to fuel the growth of galaxies and black holes in massive protoclusters.

scholarly journals A Note on the Observational Evidence for the Existence of Event Horizons in Astrophysical Black Hole Candidates

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
Cosimo Bambi
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Electromagnetic Radiation ◽  
Event Horizon ◽  
Observational Evidence ◽  
Short Paper ◽  
Event Horizons ◽  
Internal Region ◽  
The Universe ◽  
Black Hole Candidates

Black holes have the peculiar and intriguing property of having an event horizon, a one-way membrane causally separating their internal region from the rest of the Universe. Today, astrophysical observations provide some evidence for the existence of event horizons in astrophysical black hole candidates. In this short paper, I compare the constraint we can infer from the nonobservation of electromagnetic radiation from the putative surface of these objects with the bound coming from the ergoregion instability, pointing out the respective assumptions and limitations.

Black hole fusion made easy

2016 ◽  
Vol 25 (12) ◽  
pp. 1644015
Author(s):  
Roberto Emparan ◽  
Marina Martínez
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Event Horizon ◽  
Critical Behavior ◽  
Equivalence Principle ◽  
The Other ◽  
Schwarzschild Solution ◽  
Null Geodesics ◽  
Light Rays

The fusion of two black holes — a signature phenomenon of General Relativity — is usually regarded as a process so complex that nothing short of a supercomputer simulation can accurately capture it. In this essay, we explain how the event horizon of the merger can be found in an exact analytic way in the limit where one of the black holes is much smaller than the other. Remarkably, the ideas and techniques involved are elementary: the equivalence principle, null geodesics in the Schwarzschild solution, and the notion of event horizon itself. With these, one can identify features such as the line of caustics at which light rays enter the horizon, and find indications of universal critical behavior when the two black holes touch.

scholarly journals Black hole shadows in M-theory scenarios

2021 ◽  
Vol 30 (04) ◽  
pp. 2150026
Author(s):  
A. Belhaj ◽  
M. Benali ◽  
A. El Balali ◽  
W. El Hadri ◽  
H. El Moumni ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Moduli Space ◽  
Emission Rate ◽  
Rotation Parameter ◽  
High Energies ◽  
Energy Emission ◽  
M Theory

We study the shadows of four-dimensional black holes in M-theory inspired models. We first inspect the influence of M2-branes on such optical aspects for nonrotating solutions. In particular, we show that the M2-brane number can control the circular shadow size. This geometrical behavior is distorted for rotating solutions exhibiting cardioid shapes in certain moduli space regions. Implementing a rotation parameter, we analyze the geometrical shadow deformations. Among others, we recover the circular behaviors for a large M2-brane number. Investigating the energy emission rate at high energies, we find, in a well-defined approximation, that the associated peak decreases with the M2-brane number. Moreover, we investigate a possible connection with observations (from Event Horizon Telescope or future devices) from a particular M-theory compactification by deriving certain constraints on the M[Formula: see text]-brane number in the light of the [Formula: see text] observational parameters.

scholarly journals Gravitational Force between the Black Hole and Light Particle in XRBs

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Dipo Mahto ◽  
Md Shams Nadeem ◽  
Mahendra Ram ◽  
Kumari Vineeta
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Gravitational Force ◽  
Research Paper ◽  
Light Particle ◽  
X Ray ◽  
X Ray Binaries

The present research paper derives a formula for gravitational force acting between the black hole and light particle passing near the radius of event horizon of black holes and calculates also their values of different test black holes existing in only X-ray binaries (XRBs).

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