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This paper deals with the study of quasi-spherical gravitational collapse in the framework of f(R,T) theory. We will divide geometry of the star into two distinct portions i.e. interior portion and exterior portion. In the interior portion, we consider quasi-spherical Szekeres line element and in the exterior portion we take Vaidya line element. The interior and exterior portions will be glued by using Israel’s junction conditions [W. Israel, Il Nuovo Cimento B (1965–1970) 44, 1 (1966); W. Israel, Phys. Lett. A 24, 184 (1967)]. The field equations will be derived in the context of f(R,T) theory for a particular model. Apparent horizons and their time configuration for various desirable cases will also be discussed. [ABSTRACT FROM AUTHOR]

In the region where the gravitational field is strong, we have examined the influence of different gravities on the accretion disk formed due to spherical accretion. To achieve this, we obtain numerical solutions of the GRH equations, utilizing Schwarzschild, Kerr, Einstein–Gauss–Bonnet, and Hartle–Thorne spacetime metrics. We investigate the impact of the rotation parameter of a black hole (a∕M), the EGB coupling constant (α), and the quadrupole moment of the rotating black hole (q) on the accretion disk formed in a strong field. The formation of the disk for the slowly and rapidly rotating black hole models is separately examined, and comparisons are made. Our numerical simulations reveal that, under the specific conditions, the solution derived from Hartle–Thorne gravity converges toward solutions obtained from Kerr and other gravitational models. In the context of the slowly rotating black hole with a∕M=0.28, we observe a favorable agreement between the Hartle–Thorne result and the Kerr result within the range of 01, it becomes apparent that the Hartle–Thorne solution diverges from solutions provided by all gravitational models. Our motivation here is to utilize the Hartle–Thorne spacetime metric for the first time in the numerical solutions of the GRH equations for the black holes, compare the results with those obtained using other gravities, and identify under which conditions the Hartle–Thorne solution is compatible with known black hole spacetime metric solutions. This may allow us to provide an alternative perspective in explaining observed X-ray data. [ABSTRACT FROM AUTHOR]

The impact of winds and jet-inflated bubbles driven by active galactic nuclei (AGN) are believed to significantly affect the host galaxy's interstellar medium (ISM) and regulate star formation. To explore this scenario, we perform a suite of hydrodynamic simulations to model the interaction between turbulent star-forming clouds and highly pressurized AGN-driven outflows, focusing on the effects of self-gravity. Our results demonstrate that the cloudlets fragmented by the wind can become gravitationally bound, significantly increasing their survival time. While external pressurization leads to a global collapse of the clouds in cases of weaker winds (⁠|$10^{42}\!-\!10^{43}~{\rm erg\, s^{-1}}$|⁠), higher power winds (⁠|$10^{44}\!-\!10^{45}~{\rm erg\, s^{-1}}$|⁠) disperse the gas and cause localized collapse of the cloudlets. We also demonstrate that a kinetic energy-dominated wind is more efficient in accelerating and dispersing the gas than a thermal wind with the same power. The interaction can give rise to multiphase outflows with velocities ranging from a few 100 to several 1000  |${\rm km\, s^{-1}}$|⁠. The mass outflow rates are tightly correlated with the wind power, which we explain by an ablation-based mass-loss model. Moreover, the velocity dispersion and the virial parameter of the cloud material can increase by up to one order of magnitude through the effect of the wind. Even though the wind can suppress or quench star formation for about 1 Myr during the initial interaction, a substantial number of gravitationally bound dense cloudlets manage to shield themselves from the wind's influence and subsequently undergo rapid gravitational collapse, leading to an enhanced star formation rate. [ABSTRACT FROM AUTHOR]

This paper presents a novel class of interior solutions for anisotropic stars under the imposition of a self-similar symmetry. This means proposing exact solutions to the Einstein field equations to describe charged matter distribution with radiation flow. The Einstein–Maxwell system by employing specific choices of mass function is formulated to describe the gravitational collapse of charged, anisotropic, spherically symmetric distributions using the Schwarzschild metric. Two ordinary differential equations governing the dynamics are derived by matching a straightforward solution of the symmetry equations to the charged exterior (Reissner–Nordström–Vaidya). Models with satisfactory physical behavior are constructed by extensively exploring self-similar solutions for a set of parameters and initial conditions. Finally, the paper presents the evolution of physical variables and the collapsing radius, demonstrating the inevitable collapse of the matter distribution. [ABSTRACT FROM AUTHOR]

Electron-capture-supernovae (EC-SNe) provide an alternative channel for producing neutron stars (NSs). They play an important role in the formation of double NS (DNS) systems and the chemical evolution of galaxies, and contribute to the NS mass distribution in observations. It is generally believed that EC-SNe originate from e -captures on |$\rm ^{24}Mg$| and |$\rm ^{20}Ne$| in the massive degenerate oxygen–neon (ONe) cores with masses close to the Chandrasekhar limit (M Ch). However, the origin of EC-SNe is still uncertain. In this paper, we systematically studied the EC-SNe in NS + He star systems by considering the explosive oxygen burning that may occur in the near- M Ch ONe core. We provided the initial parameter spaces for producing EC-SNe in the initial orbital period − initial He star mass (log |$P_{\rm orb}^{\rm i}-M_{\rm He}^{\rm i}$|⁠) diagram, and found that both |$M_{\rm He}^{\rm i}$| and minimum |$P_{\rm orb}^{\rm i}$| for EC-SNe increase with metallicity. Then, by considering NS kicks added to the newborn NS, we investigated the properties of the formed DNS systems after the He star companions collapse into NSs, such as the orbital periods, eccentricities, and spin periods of recycle pulsars (P spin), etc. The results show that most of the observed DNS systems can be produced by NS kicks of |$\lesssim$| 50 km s−1. In addition, we found that NSs could accrete more material if the residual H envelope on the He star companions is considered, which can form the mildly recycled pulsars (P spin ∼ 20 ms) in DNS systems. [ABSTRACT FROM AUTHOR]

The Miocene Kaiserstuhl volcanic complex in the Rhine graben rift is known for simultaneously exposing both intrusive and erupted (pyroclastic) calciocarbonatites. This makes Kaiserstuhl a promising candidate for studying the field and genetic relations between intrusive calciocarbonatite and its eruptive equivalent, and the processes enabling eruption of the calciocarbonatite at the surface in particular. Eruptive calciocarbonatites in Kaiserstuhl are represented by carbonatite tuff and lapillistone beds covering a debrite fan on the western flank of the volcano. The debrites are interpreted as lahar (debris flow) and possibly also debris-avalanche deposits. Based on the observed textures, the debris flows were most likely derived by water dilution from debris avalanches resulting from edifice failure, which occurred in the central part of the Kaiserstuhl volcanic complex. The edifice failure ultimately exposed the intrusive system, and the carbonatite pyroclasts (lapilli and ash) were ejected from narrow vents represented by open-framework tuff-breccias aligned along the detachment scarp. Since the Ca-carbonates break down rapidly at high temperatures and low pressures, calciocarbonatites are unlikely to form surface lavas. On the other hand, the presence of the calciocarbonatite pyroclastic deposits suggests that some geological process faster than the high-temperature breakdown of Ca-carbonate may facilitate calciocarbonatite eruption. We suggest that the sudden exposure and decompression of a suprasolidus high-level carbonatite intrusion by edifice collapse may be a suitable scenario enabling calciocarbonatite eruption. The absence of edifice failures on alkaline volcanoes, where carbonatite intrusion is either supposed or exposed, may explain the overall scarcity of erupted calciocarbonatites. [ABSTRACT FROM AUTHOR]

An hourglass-shaped magnetic field pattern arises naturally from the gravitational collapse of a star-forming gas cloud. Most studies have focused on the prestellar collapse phase, when the structure has a smooth and monotonic radial profile. However, most observations target dense clouds that already contain a central protostar, and possibly a circumstellar disk. We utilize an analytic treatment of the magnetic field along with insights gained from simulations to develop a more realistic magnetic field model for the protostellar phase. Key elements of the model are a strong radial magnetic field in the region of rapid collapse, an off-center peak in the magnetic field strength (a consequence of magnetic field dissipation in the circumstellar disk), and a strong toroidal field that is generated in the region of rapid collapse and outflow generation. A model with a highly pinched and twisted magnetic field pattern in the inner collapse zone facilitates the interpretation of magnetic field patterns observed in protostellar clouds. [ABSTRACT FROM AUTHOR]

This work investigates the role of the Weyl tensor in the formation of a black hole. We discuss the development of the Weyl tensor and prove its existence in spacetime during the gravitational collapse of cosmic objects, utilizing the Riemannian curvature tensor, Ricci tensor, Kulkarni-Nomizu product, and Schouten tensor. By decomposing the Weyl tensor, we use theorems and proofs that satisfy the exact solutions of the Einstein field equations. We observe that the Riemann curvature tensor and Weyl tensor share the same symmetric identities, as trW(δ, .)σ = 0 such that Wδσγτ = 0 when Riemannian curvature tensor, Rδσγτ = 0. Additionally, the Riemann curvature and Weyl scalar tensor invariants are conformally related to each other, as Rδσγτ Rδσγτ = WδσγτWδσγτ = ... in the Schwarzschild metric. From the Einstein field equations, the Ricci tensor is Rστ = 0; consequently, the stress-energy tensor, Tστ = 0, indicating that the Einstein field equation is empty space. However, in the Schwarzschild black hole solution, the Ricci tensor vanishes, but the Weyl tensor does not. Additionally, it seems that divergence occurs around the event horizon in a stagnant and uncharged Schwarzschild black hole with proper acceleration. Furthermore, the investigation into the existence of the Weyl tensor in the Schwarzschild black hole reveals its presence. We also explore the Reissner-Nordström, Kerr, and Kerr-Newman black holes by examining the coupling between the Einstein-Maxwell field equations and the Weyl tensor, utilizing small Weyl corrections. We obtain the metric that reduces to the Kerr-Newman black hole solution in Boyer-Lindquist coordinates when α = 0. The same metric equation obtained reduces to Kerr black hole solutions when the electric charge q = 0 and the coupling parameter α = 0. Furthermore, when the parameter of the charged rotating black hole a vanishes, we obtain solutions for the static and spherically symmetric black hole with Weyl corrections. When the terms a = q = 0, the obtained metric reduces to the Schwarzschild black hole solution. [ABSTRACT FROM AUTHOR]

The process of the gravitational collapse might lead not only to a black hole but also to naked singularity formation. In this paper, we consider the generalized Vaidya spacetime with polytropic and generalized polytropic equations of state. We solve the Einstein and Einstein–Maxwell equations to obtain the explicit form of a mass function. We consider the limiting cases of solutions and find out, that generalized Vaidya spacetime might behave like Vaidya–de Sitter and Bonnor–Vaidya–de sitter solutions. Moreover, we explicitly show, that the part of solution, which depends on the polytropic index, is similar to cosmological fields surrounding both Vaidya and Bonnor–Vaidya black holes. The process of the gravitational collapse has been then considered. We have found out that the conditions of the naked singularity formation don't depend on the polytropic index. [ABSTRACT FROM AUTHOR]

This work presents an anisotropic cylindrical source's gravitational expansion and collapse with the cosmological constant. For this purpose, we use the cylindrical symmetric metric and energy–momentum tensor to achieve Einstein's field equation component. The mass function is also used to assess the state of the trapped surface. The parametric form of the auxiliary solution is discovered. These presumptions enable us to examine the parameter range at the positive and negative expansion scalar transitions. The generated solution produces expanding and collapsing solutions correspondingly for positive and negative parameter values. A dimensionless measure of anisotropy, pressures and energy density are utilized as physical quantities. The included parameters are shown graphically. The cosmological constant has impacted both the expansion and collapse solutions to phenomena. [ABSTRACT FROM AUTHOR]

Super-Eddington accretion of neutron stars (NSs) has been suggested both observationally and theoretically. In this paper, we propose that NSs in close-orbit binary systems with companions of helium (He) stars, most of which systems form after the common-envelope phase, could experience super-Eddington stable Case BB/BC mass transfer (MT), and can sometimes undergo accretion-induced collapse (AIC), resulting in the formation of lower mass-gap black holes (mgBHs). Our detailed binary evolution simulations reveal that AIC events tend to happen if the primary NSs have an initial mass |${\gtrsim} 1.7\, {\rm M}_\odot$| with a critical accretion rate of ≳300 times the Eddington limit. These mgBHs would have a mass nearly equal to or slightly higher than the NS maximum mass. The remnant mgBH–NS binaries after the core collapses of He stars are potential progenitors of gravitational-wave (GW) sources. Multimessenger observations between GW and kilonova signals from a population of high-mass binary NS and mgBH–NS mergers formed through super-Eddington stable MT are helpful in constraining the maximum mass and equation of state of NSs. [ABSTRACT FROM AUTHOR]

A new solution to the Einstein–Maxwell field equations for a charged anisotropic compact star is generated. The presence of both a conformal Killing vector and a quadratic equation of state give rise to a new solution with astrophysical significance. The incorporation of the conformal Killing vector leads to an equation relating the gravitational potentials. By combining the quadratic equation of state with the Einstein–Maxwell field equations, an equation for electric field intensity is obtained. Subsequently, one of the gravitational potentials is chosen on physical merits to obtain the second gravitational potential and other matter variables. The generated solution undergoes a thorough analysis to ensure acceptance of physical conditions for realistic compact star models. A deep analysis of the physical aspects reveals the well-behaved nature of the gravitational potentials and matter variables. A smooth matching of the interior and exterior metrics is achieved at the boundary. The gravitational potentials are free from physical and geometric singularities. Also, the energy conditions are satisfied, and the ratio of mass to radius and the surface redshifts remain within reasonable ranges. The equilibrium is attained by the balanced natural interior physical forces. The stability of the model against gravitational collapse is satisfied. Interestingly, the use of quadratic equation of state in conformal stars is missing in treatments performed in the past. [ABSTRACT FROM AUTHOR]

Combining quantum theory with the fundamental principles of gravity results in the modification of the uncertainty principle. In this study, we employ the extended uncertainty principle (EUP) with the maximum length derived from the cosmological particle horizon. The impact of this specific kind of modification is examined in a non-interacting electron gas system. We analytically derive the generalized relations for the degeneracy pressure and the bulk modulus. An intriguing finding is that the degeneracy pressure is reduced, as confirmed by the observed size of white dwarfs, which is smaller than what is predicted by the standard theory. Nevertheless, it is still capable of providing support against gravitational collapse. [ABSTRACT FROM AUTHOR]

The current paper studied the dynamics of shear‐free and spherically symmetric collapsing stars by incorporating the features of anisotropic dissipative fluid in the realm of f(R)$f(R)$ gravity. A complete radiative star model that describes the early static configuration obeying the embedding class 1 approach is generated. To acquittance the exact solutions of the geometric variables, a specific form of pressure anisotropy along with a time‐dependent Karmarkar condition is employed, leading to a spacetime solution that seems to be potentially reliable and regular throughout the collapse process. The matching conditions have been thoroughly investigated between the interior geometry and the Vaidya outgoing solution over the junction interface. The physical attributes of our solutions to the Einstein field equations under two viable and cosmologically well‐consistent models of f(R)$f(R)$ are manifested. The presented features are in a stable equilibrium state and sustainable to model a dynamic structure of gravitational collapse without forming the black hole. The current paper studied the dynamics of shear‐free and spherically symmetric collapsing stars by incorporating the features of anisotropic dissipative fluid in the realm of f(R) gravity. A complete radiative star model that describes the early static configuration obeying the embedding class 1 approach is generated. To acquittance the exact solutions of the geometric variables, a specific form of pressure anisotropy along with a time‐dependent Karmarkar condition is employed, leading to a spacetime solution that seems to be potentially reliable and regular throughout the collapse process. The matching conditions have been thoroughly investigated between the interior geometry and the Vaidya outgoing solution over the junction interface. The physical attributes of our solutions to the Einstein field equations under two viable and cosmologically well‐consistent models of f(R) are manifested. The presented features are in a stable equilibrium state and sustainable to model a dynamic structure of gravitational collapse without forming the black hole. [ABSTRACT FROM AUTHOR]

In this paper, in the classical framework, the lower bounds for the sensitivities of the generalized Lemaitre Tolman Bondi metric are evaluated. The calculated lower bounds via the linear dynamical systems L∂∂θ$L_{\frac{\partial }{\partial \theta }}$, L∂∂r$L_{\frac{\partial }{\partial r}}$, and L∂∂ϕ$L_{\frac{\partial }{\partial \phi }}$ are −ln2+ln|(ṘB)2−(R′)2|−2ln|B|$-\ln 2+\ln|{(\dot{R}B)}^{2}-{(R^{\prime })}^{2}|-2\ln|B|$, 2ln|Ḃ|−ln2$2\ln|\dot{B}|-\ln 2$ and −ln2−2ln|B|+ln|(Ṙ2B2−R′2)sin2θ−B2cos2θ|$-\ln 2-2\ln|B|+ \ln |(\dot{R}^{2}B^{2}-R^{\prime 2})\sin ^{2}\theta -B^{2}\cos ^{2}\theta|$ respectively. The sensitivities and the lower sensitivities via L∂∂t$L_{\frac{\partial }{\partial t}}$ are zero are also shown. In the quantum framework, the properties of the Einstein‐Vaz shells which are the final result of the quantum gravitational collapse arising from the Lemaitre Tolman Bondi discussed by Vaz in 2014 are analyzed. In fact, Vaz showed that continued collapse to a singularity can only be obtained if one combines two independent and entire solutions of the Wheeler‐DeWitt equation. Forbidding such a combination leads naturally to matter condensing on the Schwarzschild surface during quantum collapse. In that way, an entirely new framework for black holes (BHs) has emerged. The approach of Vaz was also consistent with Einstein's idea in 1939 of the localization of the collapsing particles within a thin spherical shell. Here, following an approach of oned of us (CC), we derive the BH mass and energy spectra via a Schrodinger‐like approach, by further supporting Vaz's conclusions that instead of a spacetime singularity covered by an event horizon, the final result of the gravitational collapse is an essentially quantum object, an extremely compact "dark star". This "gravitational atom" is held up not by any degeneracy pressure but by quantum gravity in the same way that ordinary atoms are sustained by quantum mechanics. Finally, the time evolution of the Einstein‐Vaz shells is discussed. In this paper, in the classical framework, the lower bounds for the sensitivities of the generalized Lemaitre Tolman Bondi metric are evaluated. In the quantum framework, the properties of the Einstein‐Vaz shells which are the final result of the quantum gravitational collapse arising from the Lemaitre Tolman Bondi discussed by Vaz in 2014 are analyzed. In fact, Vaz showed that continued collapse to a singularity can only be obtained if one combines two independent and entire solutions of the Wheeler‐DeWitt equation. Forbidding such a combination leads naturally to matter condensing on the Schwarzschild surface during quantum collapse. In that way, an entirely new framework for black holes (BHs) has emerged. The approach of Vaz was also consistent with Einstein's idea in 1939 of the localization of the collapsing particles within a thin spherical shell. Here, following an approach of oned of us (CC), we derive the BH mass and energy spectra via a Schrodinger‐like approach, by further supporting Vaz's conclusions that instead of a spacetime singularity covered by an event horizon, the final result of the gravitational collapse is an essentially quantum object, an extremely compact "dark star". This "gravitational atom" is held up not by any degeneracy pressure but by quantum gravity in the same way that ordinary atoms are sustained by quantum mechanics. Finally, the time evolution of the Einstein‐Vaz shells is discussed. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the mass accretion properties in the innermost regions of a viscously evolved protoplanetary disk and try to find some clues to the outburst events. In our newly developed one-dimensional time-dependent disk model based on the diffusion equation for surface density, we take into account the following physical effects: the gravitational collapse of the parent molecular cloud core, the irradiation from the central star to the disk, the effect of the photoevaporation mechanism, the viscosity due to the magnetorotational instability (MRI) and the gravitational instability (GI), and the thermal ionization mechanism in the inner regions. We find that the mass accretion rate M · d i s k in the innermost regions is statistically high enough to generate outbursts, although there are regions where the accretion rate is low. Additionally, we find that there is a weak correlation between the high mass accretion rate M · d i s k and the molecular cloud core's properties (angular velocity ω and mass M cd ), as well as a strong correlation with the minimum viscosity parameter α min . In general, there are two regions of outburst, the inner Region I and outer Region II. The outburst of Region I is caused by the MRI mechanism and thermal instability, while neither the MRI, the GI, nor the thermal instability causes the outburst of Region II. Our analysis suggests that the outer Region II is dominated by, or largely related to, the Rosseland mean opacity κ R and the α min parameter. [ABSTRACT FROM AUTHOR]

We present the first new type of solution of the pulsar equation since 1999. In it, the whole magnetosphere is confined inside the light cylinder and an electrically charged layer wraps around it and holds it together. The reason this new solution has never been obtained before is that all current time-dependent simulations are initialized with a vacuum dipole configuration that extends to infinity; thus, their final steady-state solution also extends to infinity. Under special conditions, such a confined configuration may be attained when the neutron star first forms in the interior of a collapsing star during a supernova explosion, or when it accretes from an external wind or disk from a donor star. It is shown that this new maximally closed non-decelerating solution is the limit of a continuous sequence of standard magnetospheres with open and closed field lines when the amount of open field lines gradually drops to zero. The minimum energy solution in this sequence is a standard magnetosphere in which the closed field line region extends up to about 80 % of the light cylinder. We estimate that the released energy when the new solution transitions to the minimum energy one is enough to power a fast radio burst. [ABSTRACT FROM AUTHOR]

Outflows play a pivotal role in star formation as one of its most visible markers and a means of transporting mass, momentum, and angular momentum from the infalling gas into the surrounding molecular cloud. Their wide reach (at least thousands of astrnomical units) is a contrast to typical disk sizes (∼10–100 au). We employ high-resolution three-dimensional nested-grid nonideal magnetohydrodynamic (MHD) simulations to study outflow properties in the Class 0 phase. We find that no disk wind is driven from the extended centrifugal disk that has weak magnetic coupling. The low-velocity winds emerge instead from the infalling magnetic pseudodisk. Much of the disk actually experiences an infall of matter rather than outflowing gas. Some of the pseudodisk wind (PD-wind) moves inward to regions above the disk and either falls onto the disk or proceeds upward. The upward flow gives the impression of a disk wind above a certain height even if the gas is originally emerging from the pseudodisk. The PD-wind has the strongest flow coming from a disk interaction zone that lies just outside the disk and is an interface between the inwardly advected magnetic field of the pseudodisk and the outwardly diffusing magnetic field of the disk. The low-velocity wind exhibits the features of a flow driven by the magnetic pressure gradient force in some regions and those of a magnetocentrifugal wind in other regions. We interpret the structure and dynamics of the outflow zone in terms of the basic physics of gravity, angular momentum, magnetic fields, and nonideal MHD. [ABSTRACT FROM AUTHOR]

The analysis of the continual gravitational contraction of a spherically symmetric shell of charged radiation is extended to higher dimensions in Einstein–Gauss–Bonnet gravity. The spacetime metric, which is of Boulware–Deser type, is real only up to a maximum electric charge and thus collapse terminates with the formation of a branch singularity. This branch singularity divides the higher dimensional spacetime into two regions, a real and physical one, and a complex region. This is not the case in neutral Einstein–Gauss–Bonnet gravity as well as general relativity. The charged gravitational collapse process is also similar for all dimensions N ≥ 5 unlike in the neutral scenario where there is a marked difference between the N = 5 and N > 5 cases. In the case where N = 5 uncharged collapse ceases with the formation of a weaker, conical singularity which remains naked for a time depending on the Gauss–Bonnet invariant, before succumbing to an event horizon. The similarity of charged collapse for all higher dimensions is a unique feature in the theory. The sufficient conditions for the formation of a naked singularity are studied for the higher dimensional charged Boulware–Deser spacetime. For particular choices of the mass and charge functions, naked branch singularities are guaranteed and indeed inevitable in higher dimensional Einstein–Gauss–Bonnet gravity. The strength of the naked branch singularities is also tested and it is found that these singularities become stronger with increasing dimension, and no extension of spacetime through them is possible. [ABSTRACT FROM AUTHOR]

During the SN1987A explosion on February 23, 1987, four underground neutrino detectors and two gravitational antennas in Rome and Maryland detected signals associated with the gravitational collapse of the star's core. Because it is impossible to detect direct gravitational radiation from the collapse of SN1987A with antennas, it is still unclear what events were recorded by gravitational antennas. In this work, an amplitude analysis of the signals from gravitational antennas in Rome and Maryland in the vicinity of the signals from neutrino detectors during Supernova SN1987A was carried out. It is shown that the amplitude distributions in all antenna signals are consistent with the distribution of fluctuating energy losses of atmospheric muons crossing the antennas. A conclusion has been made about the muon origin of signals Weber type antennas, aluminized cylinders with a mass of 2–3 t. [ABSTRACT FROM AUTHOR]

In gravitational collapses, the horizon and singularity's realisation in the finite future of the proper time used co-moving observer happens in the future of infinitely far away future of the normal time used outside probe. To the latter the horizon and singularity defined in the singularity theorem are physical realities only in the sense of uncertainty principle and ensemble interpretation. We provide two exact time dependent solution families to the Einstein equation and show that they form a pair of complementary description for the microscopic state of black holes by showing that the Bekenstein–Hawking entropy formula follows properly from their canonical wave function's degeneracy. We also develop an eXact One Body method for general relativity two-body dynamics whose conservative part calls no post newtonian approximation as input and applies to the full three stages of black hole binary merger events. By this method, we analytically calculate the gravitational wave forms following from such merger processes. In the case black holes carry exact and apriori horizon and singularity our wave forms agree with those following from conventional effective one body method but exhibit more consistent late time behaviour. In the case black holes carry only asymptotic horizon and extended inner structure thus experiencing banana shape deformation as the merger occurs, our wave forms exhibit all features especially the late time quasi-normal mode type oscillation seen in real observations. [ABSTRACT FROM AUTHOR]

The cosmic web consists of a nested hierarchy of structures: voids, walls, filaments, and clusters. These structures interconnect and can encompass one another, collectively shaping an intricate network. Here we introduce the Hierarchical Spine (H-Spine) method, a framework designed to hierarchically identify and characterize voids, walls, and filaments. Inspired by the geometrical and dynamical constraints imposed by anisotropic gravitational collapse, the H-Spine method captures the geometry and interconnectivity between cosmic structures as well as their nesting relations, offering a more complete description of the cosmic web compared to single-scale or multiscale approaches. To illustrate the method's utility, we present the distribution of densities and sizes of voids, walls, and filaments identified in a three-level hierarchical space. This analysis demonstrates how each level within the hierarchy unveils distinctive densities and scales inherent to cosmic web elements. [ABSTRACT FROM AUTHOR]

In this paper we review the possible mechanisms for the production of primordial black holes (PBHs) during a slow-reheating period in which the energy transfer of the inflaton field to standard model particles becomes effective at slow temperatures, offering a comprehensive examination of the theoretical foundations and conditions required for each of formation channel. In particular, we focus on post-inflationary scenarios where there are no self-resonances and the reheating epoch can be described by the inflaton evolving in a quadratic-like potential. In the hydrodynamical interpretation of this field during the slow-reheating epoch, the gravitational collapse of primordial fluctuations is subject to conditions on their sphericity, limits on their spin, as well as a maximum velocity dispersion. We show how to account for all conditions and show that PBHs form with different masses depending on the collapse mechanism. Finally we show, through an example, how PBH production serves to probe both the physics after primordial inflation, as well as the primordial powerspectrum at the smallest scales. [ABSTRACT FROM AUTHOR]

We compare the molecular cloud properties in subgalactic regions of two galaxies, barred spiral NGC 1313, which is forming many massive clusters, and flocculent spiral NGC 7793, which is forming significantly fewer massive clusters despite having a similar star formation rate to NGC 1313. We find that there are larger variations in cloud properties between different regions within each galaxy than there are between the galaxies on a global scale, especially for NGC 1313. There are higher masses, line widths, pressures, and virial parameters in the arms of NGC 1313 and the center of NGC 7793 than in the interarm and outer regions of the galaxies. The massive cluster formation of NGC 1313 may be driven by its greater variation in environment, allowing more clouds with the necessary conditions to emerge, although no one parameter seems primarily responsible for the difference in star formation. Meanwhile NGC 7793 has clouds that are as massive and have as much kinetic energy as the clouds in the arms of NGC 1313, but have densities and pressures more similar to those in the interarm regions and so are less inclined to collapse and form stars. The cloud properties in NGC 1313 and NGC 7793 suggest that spiral arms, bars, interarm regions, and flocculent spirals each represent distinct environments with regard to molecular cloud populations. We see surprisingly little difference in surface density between the regions, suggesting that the differences in surface densities frequently seen between arm and interarm regions in lower-resolution studies are indicative of the sparsity of molecular clouds, rather than differences in their true surface density. [ABSTRACT FROM AUTHOR]

Black holes evolve by evaporation of their event horizon. While this process is believed to be unitary, there is no consensus on the recovery of information in black hole entropy. A missing link is a quantum of information in black hole evaporation. Distinct from Hawking radiation, we identify evaporation in entangled pairs by P 2 topology of the event horizon consistent with the Bekenstein–Hawking entropy in a uniformly spaced horizon area. It derives by continuation of P 2 in Rindler spacetime prior to gravitational collapse, subject to a tight correlation of the fundamental frequency of quasi-normal-mode ringing in gravitational and electromagnetic radiation. Information extraction from entangled pairs by detecting one over the surface spanned by three faces of a large cube carries a quantum of information 2 k B log 3 upon including measurement of spin. [ABSTRACT FROM AUTHOR]

A thorough insight into the initiation, segmentation, propagation and interaction of multitrend basin-bounding faults is crucial to restoring the growth history of the faults and clarifying the fault growth pattern and its influence on the structures developed along the margin due to the growth of the basinbounding faults, but systematic studies on the individual influence of the evolution of each fault segment on the present structure are lacking. Based on 3D seismic data, the timing and growth of multitrend basin-bounding faults were analysed using T-z plots and throw backstripping, allowing us to determine the individual effects that each fault segment evolution exerteds on the present-day configuration of the northern margin of the Nanpu Sag. The basinbounding fault is composed of the Xinanzhuang and Baigezhuang faults, and the Xinanzhuang fault comprises three linked segments with varying orientations (i.e., NE-SW, E-W, and NNE-SSW). In comparison, the Baigezhuang fault comprises only two linked NW-SE-oriented fault segments. The evolution process can be divided into three stages. (1) During the early synrift I stage, namely, the isolated fault stage, five isolated multitrend basin-bounding segments were active. (2) During the late synrift I stage, namely, the hard-linkage stage, the five segments propagated laterally and linked with each other, behaving as a single fault. Meanwhile, the NE-trending No. 5 Fault bifurcated upward from the basin-bounding fault to accommodate local stress, and the NW-trending Gaobei Fault deviated from the basin-bounding fault controlled by local stresses induced by differential activities of the multitrend fault segments under the same far-field stress. (3) During the synrift II to postrift linkage development stage, the extension orientation changed from NW-SE- to N-S, and additional displacement accumulated along the basin-bounding fault without further lateral propagation. Newly formed E-W- trending faults developed orthogonal to the extension orientation and linked with preexisting NE- or NW- trending faults, forming a complex fault zone. In addition, influenced by the geometry of the basin-bounding fault, the Laoyemiao Anticline formed by gravitational collapse under the dual action of a rollover anticline and transverse anticline. Furthermore, the evolution of the basin-bounding faults played an important role in controlling the source-to-sink system, and the transition zone was the main provenance channel formed by the segmented growth of the faults. This study provides new insight into multitrend large fault evolution, and their impact on basin development provides a comprehensive explanation of the later structures developed in polyphase rifts. [ABSTRACT FROM AUTHOR]

Radiative gravitational collapse is an important and much studied phenomenon in astrophysics. Einstein's theory of general relativity (GR) is well suited to describing such processes provided closure of the system of nonlinear differential equations is achieved. Within a perturbative scheme, the property of vanishing complexity factor is used in order to complete the description of the radiative, self-gravitating system. We show that a physically viable model may be obtained which reflects the absence of energy inhomogeneities for lower density systems, in contrast to what might be expected for more aggressive collapse processes. [ABSTRACT FROM AUTHOR]

In central Australia, an apparently coeval gneiss dome (Entia Dome) developed adjacent to a thrust belt (Arltunga Nappe Complex) within an intracratonic setting. Here we employ a combination of fieldwork, geochronology, and numerical modeling to investigate the structure and tectonic evolution of these features. We present a structural model linking an extensional domain comprising the Entia Dome, across a transitional zone containing the Bruna décollement zone and the Illogwa shear zone, into a contractional zone comprising thrusts and duplexes of the Arltunga Nappe Complex. Supported by numerical modeling, we propose a tectonic model in which the dome and nappe complex formed synchronously because of the convergent gravitational collapse of the 30-40-km-deep Paleozoic Harts Range rift. [ABSTRACT FROM AUTHOR]

A seminumerical approach proposed many years ago for describing gravitational collapse in the post-quasi-static approximation is modified in order to avoid the numerical integration of the basic differential equations the approach is based upon. For doing that we have to impose some restrictions on the fluid distribution. More specifically, we shall assume the vanishing complexity factor condition, which allows for analytical integration of the pertinent differential equations and leads to physically interesting models. Instead, we show that neither the homologous nor the quasi-homologous evolution are acceptable since they lead to geodesic fluids, which are unsuitable for being described in the post-quasi-static approximation. Also, we prove that, within this approximation, adiabatic evolution also leads to geodesic fluids, and therefore, we shall consider exclusively dissipative systems. Besides the vanishing complexity factor condition, additional information is required for a full description of models. We shall propose different strategies for obtaining such an information, which are based on observables quantities (e.g., luminosity and redshift), and/or heuristic mathematical ansatz. To illustrate the method, we present two models. One model is inspired in the well-known Schwarzschild interior solution, and another one is inspired in Tolman VI solution. [ABSTRACT FROM AUTHOR]

Stars form from the gravitational collapse of turbulent, magnetized molecular cloud cores. Our non-ideal MHD simulations reveal that the intrinsically anisotropic magnetic resistance to gravity during the core collapse naturally generates dense gravomagneto sheetlets within inner protostellar envelopes – disrupted versions of classical sheet-like pseudo-discs. They are embedded in a magnetically dominant background, where less dense materials flow along the local magnetic field lines and accumulate in the dense sheetlets. The sheetlets, which feed the disc predominantly through its upper and lower surfaces, are the primary channels for mass and angular momentum transfer from the envelope to the disc. The protostellar disc inherits a small fraction (up to 10 per cent) of the magnetic flux from the envelope, resulting in a disc-averaged net vertical field strength of 1–10 mG and a somewhat stronger toroidal field, potentially detectable through ALMA Zeeman observations. The inherited magnetic field from the envelope plays a dominant role in disc angular momentum evolution, enabling the formation of gravitationally stable discs in cases where the disc field is relatively well-coupled to the gas. Its influence remains significant even in marginally gravitationally unstable discs formed in the more magnetically diffusive cases, removing angular momentum at a rate comparable to or greater than that caused by spiral arms. The magnetically driven disc evolution is consistent with the apparent scarcity of prominent spirals capable of driving rapid accretion in deeply embedded protostellar discs. The dense gravomagneto sheetlets observed in our simulations may correspond to the 'accretion streamers' increasingly detected around protostars. [ABSTRACT FROM AUTHOR]

The Generalized Uncertainty Principle (GUP) is motivated by the premise that spacetime fluctuations near the Planck scale impose a lower bound on the achievable resolution of distances, leading to a minimum length. Inspired by a semiclassical method that integrates the GUP into the partition function by deforming its phase space, we induce a modification on the thermodynamic quantities of the MIT bag model that we propose serves as an effective semiclassical description of deconfined quark matter in a space with minimal length. We investigate the consequences of this deformation on the zero‐temperature limit, revealing a saturation limit for the energy density, pressure, and baryon number density and an overall decrease of the thermodynamic quantities which suggests an enhanced stability against gravitational collapse. These findings extend existing research on GUP‐deformed Fermi gases. Ultimately, our description introduces the effects of quantum gravity in the equations of state for compact stars in a mathematically simple manner, suggesting the potential for extension to more complex systems. [ABSTRACT FROM AUTHOR]

Here we consider the generalized Oppenheimer–Snyder collapse of a star into a four-dimensional Einstein-Gauss–Bonnet black hole as well as a class of regular black holes labeled by the polytropic index of the stellar matter. We then analyze the nature of the horizon and the corresponding surface gravity outside and inside the star. The Hayward and Nielsen–Visser dynamical surface gravity are in agreement with the one resulting from the Killing vector of the outer static metric. However, these two definitions inside the star do not coincide with the Killing surface gravity outside the star when the star crosses the event horizon. This motivates us to study the surface gravity using Fodor's approach to have a unique surface gravity at the mentioned moment. Then the extremality condition and the first law of thermodynamics are discussed at the trapping horizon of the star. [ABSTRACT FROM AUTHOR]

This paper proposes an alternative mechanism to solve the so-called missing pulsar problem, a standing paradox between the theoretical expectations about the number of pulsars that should exist in the galaxy center of the Milky Way and their absence in the observations. The mechanism is based on the transformation of incident γ rays into hybridized modes, known as axion-polaritons, which can exist inside highly magnetized quark stars with a quark matter phase known as the magnetic dual chiral density wave phase. This phase, which is favored over several other dense matter phases candidates at densities a few times nuclear saturation density, has already passed several important astrophysical tests. In the proposed mechanism, the absence of young magnetars occurs because as electromagnetic waves inside the star can only propagate through the hybridized modes, incident photons coming from a γ -ray burst get transformed into massless and massive axion polaritons by the Primakoff effect. Once thermalized, the massive axion-polaritons can self-gravitate up to a situation where their total mass overpasses the Chandrasekhar limit for these bosons, producing a mini blackhole that collapses the star. [ABSTRACT FROM AUTHOR]

High-velocity stellar collisions driven by a supermassive black hole (BH) or BH-driven disruptive collisions in dense, nuclear clusters can rival the energetics of supergiant star explosions following the gravitational collapse of their iron core. Starting from a sample of red-giant star collisions simulated with the hydrodynamics code AREPO, we generated photometric and spectroscopic observables using the nonlocal thermodynamic equilibrium time-dependent radiative transfer code CMFGEN. Collisions from more extended giants or more violent collisions (with higher velocities or smaller impact parameters) yield bolometric luminosities on the order of 1043 erg s−1 at 1 d, evolving on a timescale of a week to a bright plateau at ∼1041 erg s−1 before plunging precipitously after 20–40 d at the end of the optically thick phase. This luminosity falls primarily in the UV in the first few days, thus when it is at its maximum, and shifts to the optical thereafter. Collisions at lower velocities or from less extended stars produce ejecta that are fainter but can remain optically thick for up to 40 d if they have a low expansion rate. This collision debris shows a similar spectral evolution as that observed or modeled for Type II supernovae from blue-supergiant star explosions, differing only in the more rapid transition to the nebular phase. Such BH-driven disruptive collisions should be detectable by high-cadence surveys in the UV such as ULTRASAT. [ABSTRACT FROM AUTHOR]

A total of 64 ATOMS sources at different evolutionary stages were selected to investigate the kinematics and dynamics of gas structures under feedback. We identified dense gas structures based on the integrated intensity map of H13CO+J = 1−0 emission, and then extracted the average spectra of all the structures to investigate their velocity components and gas kinematics. For the scaling relations between the velocity dispersion, σ, the effective radius, R, and the column density, N, of all the structures, σ − N * R always has a stronger correlation compared to σ − N and σ − R. There are significant correlations between velocity dispersion and column density, which may imply that the velocity dispersion originates in gravitational collapse, also revealed by the velocity gradients. The measured velocity gradients for dense gas structures in early-stage sources and late-stage sources are comparable, indicating gravitational collapse through all evolutionary stages. Late-stage sources do not have large-scale hub-filament structures, but the embedded dense gas structures in late-stage sources show similar kinematic modes to those in early- and middle-stage sources. These results may be explained by the multi-scale hub-filament structures in the clouds. We quantitatively estimated the velocity dispersion generated by the outflows, inflows, ionized gas pressure, and radiation pressure, and found that the ionized gas feedback is stronger than other feedback mechanisms. However, although feedback from HII regions is the strongest, it does not significantly affect the physical properties of the embedded dense gas structures. Combined with the conclusions in our previous work on cloud-clump scales, we suggest that although feedback from cloud to core scales will break up the original cloud complex, the substructures of the original complex can be reorganized into new gravitationally governed configurations around new gravitational centers. This process is accompanied by structural destruction and generation, and changes in gravitational centers, but gravitational collapse is always ongoing. [ABSTRACT FROM AUTHOR]

Context. Recent Event Horizon Telescope observations of M 87* and Sgr A* strongly suggest the presence of a supermassive black hole at their respective cores. We use the semi-analytic radiatively inefficient accretion flows (RIAF) model to investigate the resulting images of the Joshi–Malafarina–Narayan (JMN-1) naked singularity and the Schwarzschild black hole. Aims. We chose the JMN-1 naked singularity model and compared the synchrotron images with the Schwarzschild solution to search for any distinct features that can distinguish the two objects and to find an alternative to the solution with a black hole. Methods. We performed general relativistic ray-tracing and radiative transfer simulations using the Brahma code to generate synchrotron-emission images using the thermal distribution function for emissivity and absorptivity. We investigated effects in the images by varying the inclination angle, the disk width, and the frequency. Results. The shadow images simulated with the JMN-1 model closely resemble those generated by the Schwarzschild black hole. The disparities between the two images are very small. We conducted simulations using various plasma parameters, but the resulting images remained largely consistent for both scenarios. This similarity is evident in the horizontal cross-sectional brightness profiles of the two scenarios. Notably, the JMN-1 model exhibits a slightly higher intensity than the Schwarzschild black hole. Conclusions. We conclude that JMN-1 is a viable substitute for the black hole scenario. This conclusion is not solely grounded in the fact that the two scenarios are indistinguishable from their respective shadow observations, but also in the consideration that JMN-1 emerges as an end state of a continual gravitational collapse. This paradigm not only allows for constraints on spacetime, but also provides a good probe for the nature of the central compact object. [ABSTRACT FROM AUTHOR]

A massive star can explode in powerful supernova (SN) and form a neutron star, but it may also collapse directly into a black hole. Understanding and predicting the final fate of such stars is increasingly important, for instance, in the context of gravitational-wave astronomy. The interior mixing of stars (in general) and convective boundary mixing (in particular) remain some of the largest uncertainties in their evolution. Here, we investigate the influence of convective boundary mixing on the pre-SN structure and explosion properties of massive stars. Using the 1D stellar evolution code MESA, we modeled single, non-rotating stars of solar metallicity, with initial masses of 5 − 70 M⊙ and convective core step-overshooting of 0.05 − 0.50 pressure scale heights. Stars were evolved until the onset of iron core collapse and the pre-SN models were exploded using a parametric, semi-analytic SN code. We used the compactness parameter to describe the interior structure of stars at core collapse and we found a pronounced peak in compactness at carbon-oxygen core masses of MCO ≈ 7 M⊙, along with generally high compactness at MCO ≳ 14 M⊙. Larger convective core overshooting will shift the location of the compactness peak by 1 − 2 M⊙ to higher MCO. These core masses correspond to initial masses of 24 M⊙ (19 M⊙) and ≳40 M⊙ (≳30 M⊙), respectively, in models with the lowest (highest) convective core overshooting parameter. In both high-compactness regimes, stars are found to collapse into black holes. As the luminosity of the pre-supernova progenitor is determined by MCO, we predict black hole formation for progenitors with luminosities of 5.35 ≤ log(L/L⊙)≤5.50 and log(L/L⊙)≥5.80. The luminosity range of black hole formation from stars in the compactness peak is in good agreement with the observed luminosity of the red supergiant star N6946 BH1, which disappeared without a bright supernova, indicating that it had likely collapsed into a black hole. While some of our models in the luminosity range of log(L/L⊙) = 5.1 − 5.5 do indeed collapse to form black holes, this does not fully explain the lack of observed SN IIP progenitors at these luminosities. This case specifically refers to the "missing red supergiant" problem. The amount of convective boundary mixing also affects the wind mass loss of stars, such that the lowest black hole masses are 15 M⊙ and 10 M⊙ in our models, with the lowest and highest convective core overshooting parameter, respectively. The compactness parameter, central specific entropy, and iron core mass describe a qualitatively similar landscape as a function of MCO, and we find that entropy is a particularly good predictor of the neutron-star masses in our models. We find no correlation between the explosion energy, kick velocity, and nickel mass production with the convective core overshooting value, but we do see a tight relation with the compactness parameter. Furthermore, we show how convective core overshooting affects the pre-supernova locations of stars in the Hertzsprung–Russell diagram (HRD) and the plateau luminosity and duration of SN IIP light curves. [ABSTRACT FROM AUTHOR]

Context. Feedback from young massive stars has an important impact on the star formation potential of their parental molecular clouds. Aims. We investigate the physical properties of gas structures under feedback in the G333 complex using data of the 13CO J = 3–2 line observed with the LAsMA heterodyne camera on the APEX telescope. Methods. We used the Dendrogram algorithm to identify molecular gas structures based on the integrated intensity map of the 13CO (3–2) emission, and extracted the average spectra of all structures to investigate their velocity components and gas kinematics. Results. We derive the column density ratios between different transitions of the 13CO emission pixel by pixel, and find the peak values N2−1/N1−0 ≈ 0.5, N3−2/N1−0 ≈ 0.3, and N3−2/N2−1 ≈ 0.5. These ratios can also be roughly predicted by the nonlocal thermodynamic equilibrium (NLTE) molecular radiative transfer code RADEX for an average H2 volume density of ~4.2 × 103 cm−3. A classical virial analysis does not reflect the true physical state of the identified structures, and we find that external pressure from the ambient cloud plays an important role in confining the observed gas structures. For high-column-density structures, velocity dispersion and density show a clear correlation that is not seen for low-column-density structures, indicating the contribution of gravitational collapse to the velocity dispersion. Branch structures show a more significant correlation between 8 μm surface brightness and velocity dispersion than leaf structures, implying that feedback has a greater impact on large-scale structures. For both leaf and branch structures, σ − N * R always has a stronger correlation compared to σ − N and σ − R. The scaling relations are stronger, and have steeper slopes when considering only self-gravitating structures, which are the structures most closely associated with the Heyer relation. Conclusions. Although the feedback disrupting the molecular clouds will break up the original cloud complex, the substructures of the original complex can be reorganized into new gravitationally governed configurations around new gravitational centers. This process is accompanied by structural destruction and generation, and changes in gravitational centers, but gravitational collapse is always ongoing. [ABSTRACT FROM AUTHOR]

Primordial black holes (PBHs) are known as one of the potential candidates for dark matter. They are expected to have formed due to the direct gravitational collapse of density fluctuations in the early Universe. In this regard, examining the merger rate of PBHs within modified theories of gravity can offer a deeper insight into their abundance. In this work, we delve into the calculation of the merger rate of PBHs within the theoretical framework of f (R) gravity. Our analysis reveals an enhancement in the merger rate of PBHs compared to that obtained from general relativity. Additionally, modulating the field strength f R0 induces shifts in the PBH merger rate, presenting a potential observational signature of modified gravity. We also explore the upper bounds on the abundance of PBHs obtained from f (R) gravity models by comparing the results with gravitational-wave and observational data. The results indicate that in certain regions not excluded by benchmarking data, the parameter space for these upper bounds may be considered reliable. [ABSTRACT FROM AUTHOR]

While the configuration of a static spherically symmetric distribution of perfect fluid in an electric field has received extensive attention in the literature, only a few works have investigated the conformally flat case. The model exhibits a remarkable property being regular or singularity free is proposed. This is unexpected given that Coulombic repulsion opposes the collapse of a star to the center generally making the center unreachable. The conformally flat geometry thus enables the approach to the center of a charged star as shown in our model. Presently there is no known reported exact model that satisfies all the elementary requirements for physical acceptability. Some reported models that have claimed to be physically reliable have been shown to be deficient. The conditions for the existence of physically relevant models and show that exact solutions satisfying the conditions exist is investigated. Then a model satisfying all the requirements with isotropic particle pressure graphically for a carefully chosen parameter space is exhibited. The model admits a barotropic equation of state. The interior spacetime is successfully matched to the exterior Reissner‐Nordstrom metric. The causality criterion as well as the adiabatic stability lower bound of Chandrasekar are shown to hold. The energy conditions are also valid within the stellar radius. Other interesting models are considered. [ABSTRACT FROM AUTHOR]

In order to unveil different features of gravitational waves due to massive objects like black hole etc., researchers primarily attempt to find the corresponding quasi normal modes from the relevant wave equations. In the present article, homotopy perturbation method (HPM) is employed to obtain the wave functions by solving wave equations for one‐dimensional potential barriers. Under this scheme (i) for constant potential barrier a generalized solution which reduces to the known solution as done by Chandrasekhar and Detweiler [Proc. R. Soc. Lond. A 344 (1975) 441] is produced, (ii) the wave equation for the Price potential [Phys. Rev. D 5 (1972) 2419; Phys. Rev. D 5 (1972) 2439] by HPM is solved. The wave functions (graphically) as well as quasi‐normal modes to those of the Press solution (1973) are compared. The present investigation is important in connection to further study related to the Zerilli potential and Regge‐Wheeler potential in case of black hole. [ABSTRACT FROM AUTHOR]

The Unruh vacuum is widely used as a quantum state to describe black hole evaporation since, near the horizon, it reproduces the physical state of a quantum field, the so-called "in-vacuum", in the case where a black hole is formed by gravitational collapse. We examine the relation between these two quantum states in the background spacetime of a Reissner–Nordström black hole (both extremal and not), highlighting the similarities and striking differences. [ABSTRACT FROM AUTHOR]

This work investigates the dynamics of a collapsing magnetic string dust and string fluid in the Plank Era via spherically symmetric rainbow geometry. The field equations are modified and solved to obtain the dynamical quantities, including mass density, pressure, string tension, and magnetic field strength. These quantities are presented graphically. The energy conditions are computed showing that all the dynamical quantities are associated with physical matter. The distance and moment of apparent horizon formation are computed. The magnetic field is found to affect the distance and moment of the apparent horizon's formation. It accelerates the collapsing process. Further, the dynamical variables are maximum in the collapsing configuration's center leading to compact object (black hole) formation. The probing particle's energy affects all the dynamical variables of the fluid in a direct proportion. This resolves the information paradox as a particle with greater energy grasps the information from a particle with lesser energy and takes it out in the real world. [ABSTRACT FROM AUTHOR]

We perform numerical magnetohydrodynamic (MHD) simulations of the gravitational collapse and fragmentation of a cylindrical molecular cloud with the help of the FLASH code. The cloud collapses rapidly along its radius without any signs of fragmentation in the simulations without magnetic field. The radial collapse of the cloud is stopped by the magnetic pressure gradient in the simulations with parallel magnetic field. Cores with high density form at the cloud's ends during further evolution. The core densities are and cm–3 in the cases with initial magnetic field strengths and G, respectively. The cores move toward the cloud's center with supersonic speeds and km/s. The sizes of the cores along the filaments radius and filament's main axis are pc and pc, pc and pc, respectively. The masses of the cores increase during the filament evolution and lie in range of . According to our results, the cores observed at the edges of molecular filaments can be a result of the filament evolution with parallel magnetic field. [ABSTRACT FROM AUTHOR]

In this study, we expand on White's model proposed in [1], which explores the post-collapse evolution of density peaks while incorporating the influence of angular momentum. Within a time scale smaller than the peak collapse, denoted as , the inner regions of the peak reach an equilibrium state, forming a cuspy profile, consistent with White's findings. However, the power-law density profile is slightly flatter, specifically , due to the incorporation of the specific angular momentum obtained from theoretical models of its evolution in CDM universes, represented as . The outcome above demonstrates the impact of angular momentum on the slope of the density profile, allowing us to reproduce a slightly flatter profile similar to the one observed in high-resolution numerical simulations, where with . Notably, our model, like the simulations, does not account for adiabatic contraction. Therefore, conducting more comprehensive simulations may yield different values for the slope of the density profile, presenting an opportunity to enhance and refine our model. [ABSTRACT FROM AUTHOR]

Production of massless scalar particles by a relativistic semitransparent mirror of finite transverse size and longitudinal thickness in (1+3)D flat spacetime is studied. The derived particle spectrum formula is applied to two specific trajectories. One is the gravitational collapse trajectory invoked in (1+1)D perfectly reflecting moving mirror literature to mimic Hawking radiation, and the other is the plasma mirror trajectory proposed to be realizable in future experiments. It is found that the finiteness of the transverse size leads to diffraction, while the nontrivial thickness amplifies the production rate. We also estimated the particle yield as ∼ 3000 in a 20-day data acquisition based on the parameters invoked in the proposed AnaBHEL experiment. [ABSTRACT FROM AUTHOR]

We show that the transformation of a time-evolving spherically symmetric metric tensor into a Painlevé–Gullstrand–Lemaître form brings forth a few curious consequences. The time evolution describes a non-singular gravitational collapse, leading to a bounce and dispersal of all the clustered matter, or a wormhole geometry for certain initial conditions. The null convergence condition is violated only at the onset of bounce or the wormhole formation. As an example, the requirements to develop a Simpson–Visser wormhole/regular black-hole geometry is discussed. The solution can be regarded as a new time-evolving twin of sonic dumb holes found in analog gravity. [ABSTRACT FROM AUTHOR]

The shadow of a black hole or a collapsing star is of great importance as we can extract important properties of the object and of the surrounding spacetime from the shadow profile. It can also be used to distinguish different types of black holes and ultra compact objects. In this work, we have analytically calculated the shadow of a higher dimensional collapsing dark star, described by higher dimensional Vaidya metric, by choosing a slightly generalized version of Misner–Sharp mass function. We have also numerically investigated the properties of the shadows of the black holes and the collapsing stars for a slightly more general mass function. Examining the potential influence of extra spatial dimensions on the shadow, we have explored the possibility of distinguishing higher dimensions from the standard four-dimensional spacetime. [ABSTRACT FROM AUTHOR]

In this paper we study the shear free spherical symmetric gravitational collapse of a charged radiating star. All the physical quantities including pressure, density are regular. Energy conditions are satisfied throughout the interior of the matter configuration. The luminosity is time independent and mass is radiated linearly. The causal and non causal temperature remain greater than that of the uncharged collapsing scenario. [ABSTRACT FROM AUTHOR]