scholarly journals Radial fall of a test particle onto an evaporating black hole

2005 ◽  
Vol 83 (10) ◽  
pp. 1001-1006 ◽  
Author(s):  
Andreas Aste ◽  
Dirk Trautmann
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Test Particle ◽  
Black Hole Physics ◽  
Difficult Problem ◽  
Numerical Calculations ◽  
Computational Point ◽  
Realistic Case ◽  
Complex Cases

A test particle falling onto a classical black hole crosses the event horizon and ends up in the singularity within finite eigentime. In the "more realistic" case of a "classical" evaporating black hole, an observer falling onto a black hole observes a sudden evaporation of the hole. This illustrates the fact that the discussion of the classical process, commonly found in the literature, may become obsolete when the black hole has a finite lifetime. The situation is basically the same for more complex cases, for example, where a particle collides with two merging black holes. It should be pointed out that the model used in this paper is mainly of academic interest, since the description of the physics near a black-hole horizon still presents a difficult problem that is not yet fully understood, but our model provides a valuable possibility for students to enter the interesting field of black-hole physics and to perform numerical calculations of their own that are not very involved from the computational point of view.PACS Nos.: 04.25.–g, 04.70.–s, 04.70.Dy

scholarly journals Multiple rings in the shadow of extremely compact objects

2021 ◽  
Author(s):  
Jingkai Wang
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Electromagnetic Waves ◽  
Black Hole Physics ◽  
Compact Objects ◽  
Simple Manner ◽  
Quantitative Evidence ◽  
Exciting Opportunity ◽  
Emission Models

The Event Horizon Telescope’s image of the M87 black hole provides an exciting opportunity to study black hole physics. Since a black hole’s event horizon absorbs all electromagnetic waves, it is difficult to actively probe the horizon’s existence. However, with the help of a family of extremely compact, horizon-less objects, named “gravastars”, whose external spacetimes are nearly identical to those of black holes, one can test the absence of event horizons: absences of additional features that arise due to the existence of the gravastar, or its surface, can be used as quantitative evidence for black holes. We apply Gralla et al. approach of studying black hole images to study the images of two types of gravastars: transparent ones and reflective ones. In both cases, the transmission of rays through gravastars, or their reflections on their surfaces, leads to more rings in their images. For simple emission models, where the redshifted emissivity of the disk is peaked at a particular radius [Formula: see text], the position of a series of rings can be related in a simple manner to light ray propagation: a ring shows up around impact parameter [Formula: see text] whenever rays incident from infinity at [Formula: see text] intersects the disk at [Formula: see text]. We show that additional rings will appear in the images of transparent and reflective gravastars. In particular, one of the additional rings for the reflective gravastar is due to the prompt reflection of light on the gravastar surface, and appears to be well separated from the others. This can be an intuitive feature, which may be reliably used to constrain the reflectivity of the black hole’s horizon.

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.

scholarly journals On the speed of a test particle inside the Schwarzschild event horizon and other kinds of black holes

2018 ◽  
Vol 50 (10) ◽  
Author(s):  
Andy T. Augousti ◽  
Paweł Gusin ◽  
Bartosz Kuśmierz ◽  
Jan Masajada ◽  
Andrzej Radosz
Keyword(s):  
Black Holes ◽  
Event Horizon ◽  
Test Particle

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.

scholarly journals Ten shades of black

2015 ◽  
Vol 24 (12) ◽  
pp. 1544007 ◽  
Author(s):  
Shahar Hod
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Radiation Spectrum ◽  
Black Hole Physics ◽  
Black Body ◽  
Black Hole Radiation ◽  
Dimensional Spacetime ◽  
Opposite Behavior ◽  
Curvature Potential ◽  
Energy Dependent

The holographic principle has taught us that, as far as their entropy content is concerned, black holes in (3 + 1)-dimensional curved spacetimes behave as ordinary thermodynamic systems in flat (2 + 1)-dimensional spacetimes. In this paper, we point out that the opposite behavior can also be observed in black-hole physics. To show this we study the quantum Hawking evaporation of near-extremal Reissner–Nordström (RN) black holes. We first point out that the black-hole radiation spectrum departs from the familiar radiation spectrum of genuine (3 + 1)-dimensional perfect black-body emitters. In particular, the would be black-body thermal spectrum is distorted by the curvature potential which surrounds the black-hole and effectively blocks the emission of low-energy quanta. Taking into account the energy-dependent gray-body factors which quantify the imprint of passage of the emitted radiation quanta through the black-hole curvature potential, we reveal that the (3 + 1)-dimensional black holes effectively behave as perfect black-body emitters in a flat (9 + 1)-dimensional spacetime.

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 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.

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