The 10th Anniversary of Galaxies: The Physics of Black Holes and Gravitational Waves

Dear Colleagues,

This Special Issue concerns both black holes (BHs) and gravitational waves (GWs). Concerning BHs, they are perhaps the most fascinating objects in the fields of astrophysics and gravitational physics. Such mysterious objects are predicted by Einstein’s general relativity (GR), but such a classical theory cannot explain all the properties of BHs. It is believed that only a more general, definitive theory of quantum gravity, which might, in principle, unify GR with quantum mechanics, will clarify all the mysteries of BHs, starting from the unsolved problem of the singularities in BH cores (the singularity theorem of R. Penrose was awarded the 2020 Nobel Prize in Physics), arriving at Hawking’s BH information paradox and to the last stages of BH evaporation, where very high energies are involved. It is indeed a general conviction that BHs consist of highly excited states, representing both the “hydrogen atom” and the “quasi-thermal emission” in quantum gravity. An intriguing consequence of TeV-scale quantum gravity could be the potential production of mini BHs in high-energy experiments, such as the LHC and beyond. From the observational point of view, one has to recall that the first BH image, at the center of the galaxy Messier 87, was published by the Event Horizon Telescope Collaboration on April 10, 2019. We invite authors to submit original research and review articles that are related to BH physics.

Potential topics include, but are not limited to:

• Classical theory of BHs;
• Singularities;
• Thermodynamics of BHs;
• Hawking radiation and semiclassical theory of BHs;
• Quantum properties of BHs;
• Information paradox;
• Last stages of BH evaporation;
• Potential production of mini BHs in high-energy experiments.

Concerning GWs, their direct observation by the LIGO Scientific Collaboration in 2015 marked the beginning of a new era in astronomy. For this direct observation, Rainer Weiss, Barry C. Barish and Kip S. Thorne were awarded the 2017 Nobel Prize in Physics. In Einstein’s GR, GWs are weak perturbations of the geometry of space–time propagating through space at the speed of light. Hence, GW detections permit the investigation of GR in a previously inaccessible regime. GWs are generated when heavy objects accelerate and, in turn, create perturbations in gravitational fields. Such perturbations, described as waves, move outward from the source and give rise to effects that, can be measured when they reach Earth, via sufficiently sensitive detectors. The effects are very weak, even in the case of BHs or neutron stars spiralling ever closer to each other, or supernovae explosions.

The large number of projects and experiments currently detecting or attempting to detect gravitational waves, plus those in planning stages, to be implemented in the future, will increase the importance of both gravitational and multi messenger astronomies in the coming decades. Gravitational waves can travel unhindered through the universe, carrying information inaccessible to photons on grandiose astrophysical processes, including some hitherto unexplored. Furthermore, more precise detections of gravitational waves will allow us to test general relativity more accurately, and perhaps will allow us to combine it with quantum mechanics. We invite authors to submit original research and review articles related to the physics of GWs.

Potential topics include, but are not limited to:

• GWs theory;
• GWs detection;
• Sources of gravitational radiation;
• Relic GWs;
• GWs in extended theories of gravity;
• New ideas to detect GWs;
• Experiments on GWs;
• Interferometers science;
• GWs data analysis;
• Quantum gravity, wave-particle aspects, and graviton;
• Indirect detection;
• Resonant antenna;
• Pulsar timing arrays.

References on BHs

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References on GWs

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Prof. Dr. Christian Corda
Guest Editor

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• black holes
• gravitational waves
• general relativity
• gravitation