scholarly journals About Black Holes

2021 ◽  
Vol 11 (1) ◽  
pp. 6-9
Author(s):  
Sankar Palchoudhury
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Field Intensity ◽  
Distant Source ◽  
Circular Area ◽  
Curve Path

All kinds of waves occur for the disturbances in the quiet gravitational field. Different waves powered differently and propagated in the gravitational field. A black hole is the higher GFI (Gravitational Field Intensity) area. The rays do not possess, coming from a distant source when pass by the black holes, adequate strength to disturb in the higher GFI area of the black holes. Naturally, the rays take on a curve path as the provision in a circular area depends on the radius (distance), keeping distance according to the lower GFI area around the black holes’ centre.

Bound orbits around modified Hayward black holes

2021 ◽  
Author(s):  
Bo Gao ◽  
Xue-Mei Deng
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Angular Momentum ◽  
Gravitational Field ◽  
Periodic Orbits ◽  
Kerr Black Hole ◽  
Periodic Oscillations ◽  
Test Particles ◽  
Spin Parameter ◽  
Bound Orbits

The neutral time-like particle’s bound orbits around modified Hayward black holes have been investigated. We find that both in the marginally bound orbits (MBO) and the innermost stable circular orbits (ISCO), the test particle’s radius and its angular momentum are all more sensitive to one of the parameters [Formula: see text]. Especially, modified Hayward black holes with [Formula: see text] could mimic the same ISCO radius around the Kerr black hole with the spin parameter up to [Formula: see text]. Small [Formula: see text] could mimic the ISCO of small-spinning test particles around Schwarzschild black holes. Meanwhile, rational (periodic) orbits around modified Hayward black holes have also been studied. The epicyclic frequencies of the quasi-circular motion around modified Hayward black holes are calculated and discussed with respect to the observed Quasi-periodic oscillations (QPOs) frequencies. Our results show that rational orbits around modified Hayward black holes have different values of the energy from the ones of Schwarzschild black holes. The epicyclic frequencies in modified Hayward black holes have different frequencies from Schwarzschild and Kerr ones. These might provide hints for distinguishing modified Hayward black holes from Schwarzschild and Kerr ones by using the dynamics of time-like particles around the strong gravitational field.

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.

3. Characterizing black holes

2015 ◽  
Author(s):  
Katherine Blundell
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Gravitational Field ◽  
Curved Spacetime ◽  
Remarkable Feature ◽  
Static Limit ◽  
Frame Dragging ◽  
Axis Of Rotation ◽  
Different Types

‘Characterizing black holes’ describes the two different types of black holes: Schwarzschild black holes that do not rotate and Kerr black holes that do. The only distinguishing characteristics of black holes are their mass and their spin. A remarkable feature of a spinning black hole is that the gravitational field pulls objects around the black hole’s axis of rotation, not merely in towards its centre—an effect called frame dragging. The static limit and ergosphere regions of black holes are also described. Einstein’s equations of General Relativity allow many different solutions describing alternative versions of curved spacetime. Could white holes and worm holes exist in our universe?

scholarly journals DISCUSSION ON SOME CHARACTERISTICS OF CHARGED BRANE-WORLD BLACK HOLES

2009 ◽  
Vol 24 (04) ◽  
pp. 719-739 ◽  
Author(s):  
M. KALAM ◽  
F. RAHAMAN ◽  
A. GHOSH ◽  
B. RAYCHAUDHURI
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Scalar Field ◽  
Brane World ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Effective Potentials ◽  
Test Particles ◽  
Jacobi Formalism

Several physical natures of charged brane-world black holes are investigated. Firstly, the timelike and null geodesics of the charged brane-world black holes are presented. We also analyze all the possible motions by plotting the effective potentials for various parameters for circular and radial geodesics. Secondly, we investigate the motion of test particles in the gravitational field of the charged brane-world black holes using the Hamilton–Jacobi formalism. We consider charged and uncharged test particles and examine their behavior in both static and nonstatic cases. Thirdly, the thermodynamics of the charged brane-world black holes are studied. Finally, it is shown that there is no phenomenon of superradiance for an incident massless scalar field for such a black hole.

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.

Black holes and thermal Green functions

1978 ◽  
Vol 358 (1695) ◽  
pp. 467-494 ◽  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Energy Density ◽  
Thermal Equilibrium ◽  
Heat Bath ◽  
High Energy ◽  
High Energy Density ◽  
Green Functions ◽  
External Gravitational Field

This paper concerns itself with the possibility of thermal equilibrium between a black hole and a heat bath implied by Hawking’s discovery of black hole emission. We argue that in an isolated box of radiation, for sufficiently high energy density a black hole will condense out. We introduce thermal Green functions to discuss this equilibrium and are able to extend the original arguments, that the equilibrium is possible based on fields interacting solely with the external gravitational field, to the case when mutual and self interactions are included.

scholarly journals Gravitational cells.The formula of the gravitational constant. Calculation of the value of the gravitational constant in the region of a black hole.

2021 ◽  
Author(s):  
Andrey Chernov
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Theoretical Basis ◽  
Gravitational Constant ◽  
Physical Constant ◽  
The Body ◽  
Huge Number ◽  
Scientific Substantiation ◽  
Schwarzschild Radius

Abstract In this study, a new concept is introduced into physics - gravitational cells. These cells are densely compressed elementary particles: a proton and an electron. The body of a black hole consists of a huge number of such cells. On this theoretical basis, using the Schwarzschild radius formula and the adapted Coulomb formula, a formula for the gravitational constant was obtained and its value in the gravitational field of black holes was calculated, 𝑮𝟎=𝟔,𝟕𝟗𝟐𝟕∙𝟏𝟎−𝟏𝟏. Also, scientific substantiation of the value of the usual gravitational constant 𝑮 was obtained. In this study, a new physical constant was determined - the mass of the gravitational cell of a black hole 𝒎𝟎=𝟏,𝟓𝟏𝟏𝟓𝟗𝟑∙ 𝟏𝟎−𝟐𝟕 kg. Based on the results of the study, conclusions were drawn regarding the gravitational mass of the proton and the electron.

scholarly journals Entropic gravity from noncommutative black holes

2017 ◽  
Vol 15 (01) ◽  
pp. 1850004 ◽  
Author(s):  
Rafael C. Nunes ◽  
Hooman Moradpour ◽  
Edésio M. Barboza ◽  
Everton M. C. Abreu ◽  
Jorge Ananias Neto
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Cosmological Constant ◽  
Black Hole Entropy ◽  
Space Time ◽  
Isotropic Universe ◽  
Entropic Gravity ◽  
The Universe

In this paper, we investigated the effects of a noncommutative (NC) space-time on the dynamics of the Universe. We generalize the black hole entropy for a NC black hole. Then, using the entropic gravity formalism, we will show that the noncommutativity changes the strength of the gravitational field. By applying this result to a homogeneous and isotropic Universe containing nonrelativistic matter and a cosmological constant, we show that the modified scenario by the noncommutativity of the space-time is a better fit to the obtained data than the standard one at 68% CL.

scholarly journals Thermodynamic approach to field equations in Lovelock gravity and f(R) gravity revisited

2014 ◽  
Vol 23 (11) ◽  
pp. 1450093 ◽  
Author(s):  
Yan-Gang Miao ◽  
Fang-Fang Yuan ◽  
Zheng-Zheng Zhang
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Black Hole Thermodynamics ◽  
Thermodynamic Approach ◽  
Field Equations ◽  
Lovelock Gravity ◽  
First Law Of Thermodynamics ◽  
Charged Black Holes ◽  
Gravitational Field Equations

The first law of thermodynamics at black hole horizons is known to be obtainable from the gravitational field equations. A recent study claims that the contributions at inner horizons should be considered in order to give the conventional first law of black hole thermodynamics. Following this method, we revisit the thermodynamic aspects of field equations in the Lovelock gravity and f(R) gravity by focusing on two typical classes of charged black holes in the two theories.

Effect of an external magnetic field on particle acceleration by a rotating black hole surrounded with quintessential energy

2018 ◽  
Vol 27 (08) ◽  
pp. 1850088 ◽  
Author(s):  
Sanjar Shaymatov ◽  
Bobomurat Ahmedov ◽  
Zdeněk Stuchlík ◽  
Ahmadjon Abdujabbarov
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
External Magnetic Field ◽  
Field Intensity ◽  
Center Of Mass ◽  
Mass Energy ◽  
Intensity Parameter ◽  
Center Of Mass Energy ◽  
Spacetime Structure

We investigate particle motion and collisions in the vicinity of rotating black holes immersed in combined cosmological quintessential scalar field and external magnetic field. The quintessential dark-energy field governing the spacetime structure is characterized by the quintessential state parameter [Formula: see text] characterizing its equation of state, and the quintessential field-intensity parameter [Formula: see text] determining the static radius where the black hole attraction is just balanced by the quintessential repulsion. The magnetic field is assumed to be test field that is uniform close to the static radius, where the spacetime is nearly flat, being characterized by strength [Formula: see text] there. Deformations of the test magnetic field in vicinity of the black hole, caused by the Ricci non-flat spacetime structure are determined. General expression of the center-of-mass energy of the colliding charged or uncharged particles near the black hole is given and discussed in several special cases. In the case of nonrotating black holes, we discuss collisions of two particles freely falling from vicinity of the static radius, or one such a particle colliding with charged particle revolving at the innermost stable circular orbit. In the case of rotating black holes, we discuss briefly particles falling in the equatorial plane and colliding in close vicinity of the black hole horizon, concentrating attention to the interplay of the effects of the quintessential field and the external magnetic field. We demonstrate that the ultra-high center-of-mass energy can be obtained for black holes placed in an external magnetic field for an infinitesimally small quintessential field-intensity parameter [Formula: see text]; the center-of-mass energy decreases if the quintessential field-intensity parameter [Formula: see text] increases.

Sign in / Sign up

Export Citation Format

Share Document