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# Open Questions in Black Hole Physics

A topical collection in *Universe* (ISSN 2218-1997). This collection belongs to the section "Gravitation".

## Editors

**Interests:**black holes; singularities; quantum fields in curved space-time; inflation; modified gravity; Palatini formalism; stellar structure models; compact objects

Special Issues, Collections and Topics in MDPI journals

**Interests:**black holes; modified gravity; cosmology; bouncing solutions; spacetime singularities; nonlinear electrodynamics; field theory; topological defects; metric-affine geometry

Special Issues, Collections and Topics in MDPI journals

## Topical Collection Information

Dear Colleagues,

Black holes are fascinating objects that hold the key to uncover the intimate relation between gravitation and the quantum, as well as a number of astrophysical phenomena. The strength of their gravitational field is responsible for extreme deformations of the causal structure of space-time, leading to intriguing thermodynamic properties and serious tensions with our understanding of the quantum world. The current picture of the Universe could hardly be explained without recurring to them, even though they are very elusive and defy direct observational detection.

The coming years are likely to witness important breakthroughs in our view of black holes and their astrophysical and quantum properties through the direct detection of gravitational waves and Hawking radiation in analogue models. A number of fundamental open questions might find an answer and new ones may emerge. Are black holes, seen as regions of space-time hidden behind an event horizon, astrophysically realizable? Are there viable compact-object alternatives? Will black hole mergers allow us to experimentally probe the strong-field gravitational regime? What happens when two singularities meet in a black hole merger? Do singularities have a physical role? Can wormholes alleviate the issue of singularities? How much can we learn about black holes from analogue models? What is the end state of black hole evaporation? Why primordial black hole explosions have not been observed yet? What aspects of black holes are modified in a quantum theory of gravity? How does a supermassive black hole interact with its host galaxy? These are just a few examples of the Open Questions in Black Hole Physics we expect to address in this Special Issue of Universe.

Dr. Gonzalo J. Olmo

Dr. Diego Rubiera-Garcia

*Collection Editors*

**Manuscript Submission Information**

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the collection website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. *Universe* is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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*r*, which on the one hand can be fit to future observational data, and on the other hand is sufficiently general so as to encompass an extremely wide class of theoretical models. In all of these spacetimes, both the timelike Hamilton–Jacobi (geodesic) and massive Klein–Gordon (wave) equations separate, and the spacetime geometry is asymptotically Kerr; hence, these spacetimes are well-suited to modeling real astrophysical black holes. The authors then prove the existence of Killing horizons for this entire class of spacetimes, and give tractable expressions for the angular velocities, areas, and surface gravities of these horizons. We emphasize the validity of rigidity results and zeroth laws for these horizons. Full article

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*Universe*

**2019**,

*5*(7), 163; https://doi.org/10.3390/universe5070163 (registering DOI) - 3 Jul 2019

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*l*. It is determined that, for some values of constants, i.e.,

*l*, collapse results in a Naked Singularity (NS) while, for some values of constants, it does not form NS or Black Hole (BH). This study presents the effect on the collapsing process for all values of

*l*. Full article

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*AdS*

_{2}/

*CFT*

_{1}and Conformal Weyl Gravity Cited by 2 | Viewed by 3431

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*s*-waves, with calculable central extensions. These centers, in conjunction with their proper regularized lowest Virasoro eigenmodes, yield the Bekenstein–Hawking black hole entropy via the statistical Cardy formula. We also analyze quantum holomorphic fluxes of the dual conformal field theories (CFTs) in the near horizon, giving rise to finite Hawking temperatures weighted by the central charges of the respective black hole spacetimes. We conclude with a discussion and outlook for future work. Full article

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*c*coefficient. Here,

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*F*(

*R*) Gravity Cited by 38 | Viewed by 4464

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*R*) Theories Cited by 94 | Viewed by 5925

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