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In this work we elaborate on some specific results contained in Ref. [1], relevant to the gravitational collapse into a singularity-free metric derived from the Asymptotically Safe Gravity framework. The final product of the collapse is a regular black hole with a central core of non-trapped surfaces, a region where light can in principle propagate freely in any direction.

The development of orogenic belts structures in the Southern-Central Tunisian Atlas is influenced by the evolution of tectonic activities during different phases, which are also closely linked to the formation of gravitational collapse structure. The typical example is that of the northern flank of the Jebel Orbata particularly the Ben Zannouch fold. It is an asymmetrical anticline interpreted by the model of “Fault Propagation Folds”. The development of the Ben Zannouch structures is resulted from landslides, scree falls and inverted layers plunging to the south. The direction of resulted gravitational structure is parallel to the main thrust direction of the Bou Omrane anticline. The thrust activity of Bou Omrane fault is associated to the important paleo-slope facing south and plastic lithology (incompetent marl layers) of outcropped series, facilitates the development of the Ben Zannouch Flap structure. The definition of gravitational collapse structures for the first time in Tunisia particularly in the northern flank of the Jebel Orbata is controlled by many principal structural conditions: fragmentation of the landslide surfaces, rheology and topography. Other regional factors can be distinguished in the Southern-Central Tunisian Atlas as the seismic activity of the pre-existing Gafsa fault reactivated during compressive phases and the weather conditions during the postglacial period.

We present high-resolution hydrodynamical simulations aimed at following the gravitational collapse of a gas core, in which a turbulent spectrum of velocity is implemented only initially. We determine the maximal value of the ratio of kinetic energy to gravitational energy, denoted here by (EkinEgrav)max, so that the core (i) will collapse around one free-fall time of time evolution or (ii) will expand unboundedly, because it has a value of larger than (EkinEgrav)max. We consider core models with a uniform or centrally condensed density profile and with velocity spectra composed of a linear combination of one-half divergence-free turbulence type and the other half of a curl-free turbulence type. We show that the outcome of the core collapse are protostars forming either (i) a multiple system obtained from the fragmentation of filaments and (ii) a single primary system within a long filament. In addition, some properties of these protostars are also determined and compared with those obtained elsewhere.

This book is a thorough and up‐to‐date introduction to black hole physics. It provides a modern and unified overview of all their aspects, physical, mathematical, astrophysical, classical, and quantum. Black holes are the most intriguing objects in the Universe. For many years they have been considered just as interesting solutions of the General Relativity with a number of amusing mathematical properties. But now, after discovery of astrophysical black holes, the Einstein gravity has become a practical tool for their study. In this book we present the theory of black holes in the form which might be useful for students and young scientists. This is a self‐contained textbook. It includes pedagogically presented `standard' material on black holes and also quite new subjects such as black holes in spacetimes with large extra dimensions and a role of hidden symmetries in black hole physics.

Recently the quantum Oppenheimer–Snyder gravitational collapse model has been proposed in loop quantum gravity, providing quantum-corrected Schwarzschild spacetimes as the exterior of the collapsing dust ball. In this paper, the quantum gravity effects on the black hole shadows in this model are studied, and the stability of the quantum-corrected black holes is also analyzed by calculating the quasinormal modes. It turns out that the quantum correction always shrinks the radius of shadows, and the quantum-corrected black holes are stable against the scalar and vector perturbations.

The production of elements by rapid neutron capture (r-process) in neutron-star mergers is expected theoretically and is supported by multimessenger observations 1 – 3 of gravitational-wave event GW170817: this production route is in principle sufficient to account for most of the r-process elements in the Universe 4 . Analysis of the kilonova that accompanied GW170817 identified 5 , 6 delayed outflows from a remnant accretion disk formed around the newly born black hole 7 – 10 as the dominant source of heavy r-process material from that event 9 , 11 . Similar accretion disks are expected to form in collapsars (the supernova-triggering collapse of rapidly rotating massive stars), which have previously been speculated to produce r-process elements 12 , 13 . Recent observations of stars rich in such elements in the dwarf galaxy Reticulum II 14 , as well as the Galactic chemical enrichment of europium relative to iron over longer timescales 15 , 16 , are more consistent with rare supernovae acting at low stellar metallicities than with neutron-star mergers. Here we report simulations that show that collapsar accretion disks yield sufficient r-process elements to explain observed abundances in the Universe. Although these supernovae are rarer than neutron-star mergers, the larger amount of material ejected per event compensates for the lower rate of occurrence. We calculate that collapsars may supply more than 80 per cent of the r-process content of the Universe. A rare type of supernova—triggered by the collapse of a rapidly rotating single star—could have provided more than 80 per cent of the r-process elements in the Universe.

The origin of super-massive black holes in the early universe remains poorly understood. Gravitational collapse of a massive primordial gas cloud is a promising initial process, but theoretical studies have difficulty growing the black hole fast enough. We report numerical simulations of early black hole formation starting from realistic cosmological conditions. Supersonic gas motions left over from the Big Bang prevent early gas cloud formation until rapid gas condensation is triggered in a protogalactic halo. A protostar is formed in the dense, turbulent gas cloud, and it grows by sporadic mass accretion until it acquires 34,000 solar masses. The massive star ends its life with a catastrophic collapse to leave a black hole—a promising seed for the formation of a monstrous black hole.

Some types of core-collapse supernovae are known to produce a neutron star (NS). A binary NS merger was recently detected from its gravitational wave emission, but it is unclear how such a tight binary system can be formed. De et al. discovered a core-collapse supernova with unusual properties, including the removal of the outer layers of the star before the explosion. They interpret this as the second supernova in an interacting binary system that already contains one NS. Because the explosion probably produced a second NS (rather than a black hole) in a tight orbit, it could be an example of how binary NS systems form. Science , this issue p. 201 An unusual core-collapse supernova appears to have formed a binary neutron star in a tight orbit. Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 10 50 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.

The necessity of quantising the gravitational field is still subject to an open debate. In this paper we compare the approach of quantum gravity, with that of a fundamentally semi-classical theory of gravity, in the weak-field non-relativistic limit. We show that, while in the former case the Schrödinger equation stays linear, in the latter case one ends up with the so-called Schrödinger-Newton equation, which involves a nonlinear, non-local gravitational contribution. We further discuss that the Schrödinger-Newton equation does not describe the collapse of the wave-function, although it was initially proposed for exactly this purpose. Together with the standard collapse postulate, fundamentally semi-classical gravity gives rise to superluminal signalling. A consistent fundamentally semi-classical theory of gravity can therefore only be achieved together with a suitable prescription of the wave-function collapse. We further discuss, how collapse models avoid such superluminal signalling and compare the nonlinearities appearing in these models with those in the Schrödinger-Newton equation.

Roger Penrose proposed that a spatial quantum superposition collapses as a back-reaction from spacetime, which is curved in different ways by each branch of the superposition. In this sense, one speaks of gravity-related wave function collapse. He also provided a heuristic formula to compute the decay time of the superposition—similar to that suggested earlier by Lajos Diósi, hence the name Diósi–Penrose model. The collapse depends on the effective size of the mass density of particles in the superposition, and is random: this randomness shows up as a diffusion of the particles’ motion, resulting, if charged, in the emission of radiation. Here, we compute the radiation emission rate, which is faint but detectable. We then report the results of a dedicated experiment at the Gran Sasso underground laboratory to measure this radiation emission rate. Our result sets a lower bound on the effective size of the mass density of nuclei, which is about three orders of magnitude larger than previous bounds. This rules out the natural parameter-free version of the Diósi–Penrose model.The radiation emission rate from gravity-related wave function collapse is calculated and the results of a dedicated experiment at the Gran Sasso laboratory are reported, ruling out the natural parameter-free version of the Diósi–Penrose model.