Shell Of Matter Research Articles

Constant velocity physical warp drive solution

Abstract Warp drives are exotic solutions of general relativity that offer novel means of transportation. In this study, we present a solution for a constant-velocity subluminal warp drive that satisfies all of the energy conditions. The solution involves combining a stable matter shell with a shift vector distribution that closely matches well-known warp drive solutions such as the Alcubierre metric. We generate the spacetime metric numerically, evaluate the energy conditions, and confirm that the shift vector distribution cannot be reduced to a coordinate transformation. This study demonstrates that classic warp drive spacetimes can be made to satisfy the energy conditions by adding a regular matter shell with a positive ADM mass.

Universal construction of black hole microstates

We refine and extend a recent construction of sets of black hole microstates with semiclassical interiors that span a Hilbert space of dimension eS, where S is the black hole entropy. We elaborate on the definition and properties of microstates in statistical and black hole mechanics. The gravitational description of microstates employs matter shells in the interior of the black hole, and we argue that in the limit where the shells are very heavy, the construction acquires universal validity. To this end, we show it for very wide classes of black holes; we first extend the construction to rotating and charged black holes, including extremal and near-extremal solutions, with or without supersymmetry, and we sketch how the construction of microstates can be embedded in string theory. We then describe how the approach can include general quantum corrections, near or far from extremality. For supersymmetric black holes, the microstates we construct differ from other recent constructions in that the interior excitations are not confined within the near-extremal throat. Published by the American Physical Society 2024

Landscape evolution of the Ganga-Sai interfluve in response to river dynamics and Late Pleistocene-Holocene climate change via a meander cut-off lake of a plains-fed channel

The floodplains in the interfluve between the Ganga and Sai rivers in the Central Ganga Plains exhibit a broad suite of geomorphic features such as a linear array of meander cut-offs and oxbows representing abandoned sinuous channels. Here we integrate regional and local scale geomorphic analysis using satellite imageries with detailed chronostratigraphic and paleoclimatic reconstruction from a large oxbow lake (Baraila Tal) in the paleochannel belt to infer landscape evolution in this region. The stratigraphic succession at Baraila Tal supported by sedimentology and stable isotope composition of organic matter and micro-gastropod shells suggests that the lake was previously a part of an active fluvial system, and the depositional environment transformed from a fluvial to a lacustrine system in response to geomorphic and climatic changes during the post-LGM period. Integrating geomorphic and paleoclimatic data, we identify four stages (I-IV) of landscape evolution in the Ganga-Sai interfluve region during the Late Pleistocene-Holocene interval: (I) active channel phase of paleo-Sai river before 12 kyr, (II) development of paleochannel belt and meander cut-offs during 12–8 kyr, (III) development of ‘misfit’ Sai river and gullied landscape during 8–7 kyr, and (IV) expansion of ephemeral lakes (wetlands) and subsequent filling post 7 kyr. We have demonstrated the use of paleoclimate and paleovegetation data retrieved from a meander cut-off lake for deciphering landscape evolution.

Smooth extensions of black holes in loop quantum gravity

Vacuum spherically symmetric loop quantum gravity in the midi-superspace approximation using inhomogeneous horizon-penetrating slices has been studied for a decade, and it has been noted that the singularity is eliminated. It is replaced by a region of high curvature and potentially large quantum fluctuations. It was recently pointed out that the effective semiclassical metric implies the existence of a shell of matter which violates energy conditions in regions where the curvature is largest. Here, we propose an alternative way of treating the problem that is free from the shells. The ambiguity in the treatment is related with the existence of new observables in the quantum theory that characterize the area excitations, and how the counterpart of diffeomorphisms in the discrete quantum theory is mapped to the continuum semiclassical picture. The resulting spacetime in the high curvature region inside the horizon is approximated by a metric of the type of the Simpson–Visser wormhole and it connects the black hole interior to a white hole in a smooth manner.

Defect Wormholes Are Defective

The various “defect wormholes” developed by Klinkhamer have recently attracted considerable attention—especially in view of the fact that the simplest example, the so-called “vacuum defect wormhole”, was claimed to be an everywhere-vacuum everywhere-Ricci-flat exact solution to the Einstein equations. This claim has been conclusively refuted by Feng, and in the current article, we take a deeper look at exactly what goes wrong. The central issue is this: Although Klinkhamer’s specific representation of the metric gab is smooth (C∞), his inverse metric gab is not even everywhere continuous (C0), being undefined at the wormhole throat. This situation implies that one should very carefully investigate curvature tensors at the throat using the Israel–Lanczos–Sen thin-shell formalism. Doing so reveals the presence of a delta-function energy-condition-violating thin shell of matter at the wormhole throat. The “defect wormholes” are thus revealed to be quite ordinary “cut-and-paste” thin-shell wormholes, but represented in a coordinate system that is unfortunately pathological at exactly the same place that all the interesting physics occurs. To help clarify the situation, we shall focus on the behavior of suitable coordinate invariants—the Ricci scalar, the eigenvalues of the mixed Rab Ricci tensor, and the eigenvalues of the mixed Rabcd Riemann tensor.

SN 2022jli: A Type Ic Supernova with Periodic Modulation of Its Light Curve and an Unusually Long Rise

We present multiwavelength photometry and spectroscopy of SN 2022jli, an unprecedented Type Ic supernova discovered in the galaxy NGC 157 at a distance of ≈ 23 Mpc. The multiband light curves reveal many remarkable characteristics. Peaking at a magnitude of g = 15.11 ± 0.02, the high-cadence photometry reveals periodic undulations of 12.5 ± 0.2 days superimposed on the 200-day supernova decline. This periodicity is observed in the light curves from nine separate filter and instrument configurations with peak-to-peak amplitudes of ≃ 0.1 mag. This is the first time that repeated periodic oscillations, over many cycles, have been detected in a supernova light curve. SN 2022jli also displays an extreme early excess that fades over ≈25 days, followed by a rise to a peak luminosity of L opt = 1042.1 erg s−1. Although the exact explosion epoch is not constrained by data, the time from explosion to maximum light is ≳ 59 days. The luminosity can be explained by a large ejecta mass (M ej ≈ 12 ± 6 M ⊙) powered by 56Ni, but we find it difficult to quantitatively model the early excess with circumstellar interaction and cooling. Collision between the supernova ejecta and a binary companion is a possible source of this emission. We discuss the origin of the periodic variability in the light curve, including interaction of the SN ejecta with nested shells of circumstellar matter and neutron stars colliding with binary companions.

Exact solution of the Einstein field equations for a spherical shell of fluid matter

We determine the exact solution of the Einstein field equations for the case of a spherically symmetric shell of liquid matter, characterized by an energy density which is constant with the Schwarzschild radial coordinate r between two values $$r_{1}$$ and $$r_{2}$$ . The solution is given in three regions, one being the well-known analytical Schwarzschild solution in the outer vacuum region, one being determined analytically in the inner vacuum region, and one being determined mostly analytically but partially numerically, within the matter region. The solutions for the temporal coefficient of the metric and for the pressure within this region are given in terms of a non-elementary but fairly straightforward real integral. For some values of the parameters this integral can be written in terms of elementary functions. We show that in this solution there is a singularity at the origin, and give the parameters of that singularity in terms of the geometrical and physical parameters of the shell. This does not correspond to an infinite concentration of matter, but in fact to zero energy density at the center. It does, however, imply that the spacetime within the spherical cavity is not flat, so that there is a non-trivial gravitational field there, in contrast with Newtonian gravitation. This gravitational field is repulsive with respect to the origin, and thus has the effect of stabilizing the geometrical configuration of the matter, since any particle of the matter that wanders out into either one of the vacuum regions tends to be brought back to the bulk of the matter by the gravitational field.

Complete solution of the Einstein field equations for a spherical distribution of polytropic matter

We determine the complete solution of the Einstein field equations for the case of a spherically symmetric distribution of gaseous matter, characterized by a polytropic equation of state. We show that the field equations automatically generate two sharp boundaries for the gas, an inner one and an outer one, given by radial positions $$r_{1}$$ and $$r_{2}$$ , and thus define a shell of gaseous matter outside of which the energy density is exactly zero. Hence this shell is surrounded by an outer vacuum region, and surrounds an inner vacuum region. Therefore, the solution is given in three regions, one being the well-known analytical Schwarzschild exterior solution in the outer vacuum region, one being determined analytically in the inner vacuum region, and one being determined partially analytically and partially numerically, within the matter region, between the two boundary values $$r_{1}$$ and $$r_{2}$$ of the Schwarzschild radial coordinate r. This solution is therefore somewhat similar to the one previously found for a spherically symmetric shell of liquid fluid, and is in fact exactly the same in the cases of the inner and outer vacuum regions. The main difference is that here the boundary values $$r_{1}$$ and $$r_{2}$$ are not chosen arbitrarily, but are instead determined by the dynamics of the system. As was shown in the case of the liquid shell, also in this solution there is a singularity at the origin, that just as in that case does not correspond to an infinite concentration of matter, but in fact to zero matter energy density at the center. Also as in the case of the liquid shell, the spacetime within the spherical cavity is not flat, so that there is a non-trivial gravitational field there, in contrast with Newtonian gravitation. This inner gravitational field has the effect of repelling matter and energy away from the origin, thus avoiding a concentration of matter at that point.

GLASS: Generator for Large Scale Structure

We present GLASS, the Generator for Large Scale Structure, a new code for the simulation of galaxy surveys for cosmology, which iteratively builds a light cone with matter, galaxies, and weak gravitational lensing signals as a sequence of nested shells. This allows us to create deep and realistic simulations of galaxy surveys at high angular resolution on standard computer hardware and with low resource consumption. GLASS also introduces a new technique to generate transformations of Gaussian random fields (including lognormal) to essentially arbitrary precision, an iterative line-of-sight integration over matter shells to obtain weak lensing fields, and flexible modelling of the galaxies sector. We demonstrate that GLASS readily produces simulated data sets with per cent-level accurate two-point statistics of galaxy clustering and weak lensing, thus enabling simulation-based validation and inference that is limited only by our current knowledge of the input matter and galaxy properties. The code described in this paper is available <a href="https://github.com/glass-dev/glass">here</a>.

GLASS: Generator for Large Scale Structure

We present GLASS, the Generator for Large Scale Structure, a new code for the simulation of galaxy surveys for cosmology, which iteratively builds a light cone with matter, galaxies, and weak gravitational lensing signals as a sequence of nested shells. This allows us to create deep and realistic simulations of galaxy surveys at high angular resolution on standard computer hardware and with low resource consumption. GLASS also introduces a new technique to generate transformations of Gaussian random fields (including lognormal) to essentially arbitrary precision, an iterative line-of-sight integration over matter shells to obtain weak lensing fields, and flexible modelling of the galaxies sector. We demonstrate that GLASS readily produces simulated data sets with per cent-level accurate two-point statistics of galaxy clustering and weak lensing, thus enabling simulation-based validation and inference that is limited only by our current knowledge of the input matter and galaxy properties.

Regge pole description of scattering by dirty black holes

We study the problem of plane monochromatic scalar waves impinging upon a Schwarzschild dirty black hole -- a Schwarzschild black hole surrounded by a thin spherical shell of matter -- using the complex angular momentum approach. We first recall general results concerning the differential scattering cross section in the classical limit through a null geodesic analysis by exploring different configurations of the shell. In particular, we show that dirty black hole spacetimes may exhibit various critical effects for geometrical optics. We compute the Regge pole spectrum for various shell configurations and show that it exhibits two or three distinct branches of poles, labelled inner surface waves, broad resonances and outer surface waves. In the latter, two sub-families have been identified, the surface waves associated with the outer light-ring and the creeping modes associated with the surface of the shell. We show, using WKB analysis, that the position of the shell sets the real part of the broad resonances while its energy-momentum and the discontinuity of the potential at the shell's surface set their imaginary part. Next, we provide the complex angular momentum representation of the differential scattering cross section and examine the role of the different Regge pole branches. We compute the differential scattering cross section for various configurations at several frequencies and show a very good agreement with the partial-wave calculations. Finally, we highlight the role of the critical effects, i.e., orbiting, glory, grazing and rainbow scattering, and their impact on the differential scattering cross section.

An analytic model for gravitational collapse of spherical matter under mixed pressure

In this paper, we investigate spherically symmetric gravitational collapse of thick matter shell without radiation in the Einstein gravity with cosmological constant. The orbit of the infalling thick matter is determined by imposing an equation of state for the matter near interface, where pressure constituted of the transverse component and the longitudinal one is proportional to energy density. We present analytic solutions for the equation of state and discuss parameter region to satisfy physical conditions such as the absence of the shell crossing singularity, the monotonic increase of the emergent infinite redshift surface and energy conditions. We finally show that adopting the definition presented in arXiv:2005.13233 the total energy in this time-dependent system is invariant under the given time evolution.

Quantum dynamics of gravitational massive shell

The quantum dynamics of a self-gravitating thin matter shell in vacuum has been considered. Quantum Hamiltonian of the system is positive definite. Within chosen set of parameters, the quantum shell bounces above the horizon. Considered quantum system does not collapse to the gravitational singularity of the corresponding classical system.

The quasi-adiabatic relaxation of haloes in the IllustrisTNG and EAGLE cosmological simulations

AbstractThe dark matter content of a gravitationally bound halo is known to be affected by the galaxy and gas it hosts. We characterize this response for haloes spanning over four orders of magnitude in mass in the hydrodynamical simulation suites IllustrisTNG and EAGLE. We present simple fitting functions in the spherically averaged quasi-adiabatic relaxation framework that accurately capture the dark matter response over the full range of halo mass and halo-centric distance we explore. We show that commonly employed schemes, which consider the relative change in radius rf/ri − 1 of a spherical dark matter shell to be a function of only the relative change in its mass Mi/Mf − 1, do not accurately describe the measured response of most haloes in IllustrisTNG and EAGLE. Rather, rf/ri additionally explicitly depends upon halo-centric distance rf/Rvir for haloes with virial radius Rvir, being very similar between IllustrisTNG and EAGLE and across halo mass. We also account for a previously unmodelled effect, likely driven by feedback-related outflows, in which shells having rf/ri ≃ 1 (i.e. no relaxation) have Mi/Mf significantly different from unity. Our results are immediately applicable to a number of semi-analytical tools for modelling galactic and large-scale structure. We also study the dependence of this response on several halo and galaxy properties beyond total mass, finding that it is primarily related to halo concentration and star formation rate. We discuss possible extensions of these results to build a deeper physical understanding of the small-scale connection between dark matter and baryons.

Classical mass inflation versus semiclassical inner horizon inflation

We analyze the geometry of a spherically symmetric black hole with an inner and outer apparent horizon that is perturbed by spherical null shells of matter. On a classical level we observe that the mass inflation instability is triggered, resulting in a growth of curvature and an inward displacement of the inner horizon. We study in detail the inner structure of the mass-inflated region and compare it with previous results obtained for the case in which the perturbing matter content has a continuous distribution. We then perform an approximate calculation of the renormalized stress-energy tensor of a quantum field in the vicinity of the inner horizon, and analyze the semiclassical backreaction on this region of the geometry. We find that the classical tendency for this horizon to move inward due to mass inflation is challenged and potentially overcome by a semiclassical tendency for it to inflate outward.

Electrically charged spherical matter shells in higher dimensions: Entropy, thermodynamic stability, and the black hole limit

We study the thermodynamic properties of a static electrically charged spherical thin shell in $d$ dimensions by imposing the first law of thermodynamics on the shell. The shell is at radius $R$, inside it the spacetime is Minkowski, and outside it the spacetime is Reissner-Nordstr\"om. We obtain that the shell thermodynamics is fully described by giving two additional reduced equations of state, one for the temperature and another for the electrostatic potential. We choose the equation of state for the temperature as a power law in the gravitational radius $r_+$ with exponent $a$, such that the $a=1$ case gives the temperature of a shell with black hole thermodynamic properties, and for the electrostatic potential we choose an equation of state characteristic of a Reissner-Nordstr\"om black hole spacetime. The entropy of the shell is found to be proportional to $A_+^a$, where $A_+$ is the gravitational area corresponding to $r_+$, with $a>0$. We are then able to perform the black hole limit $R=r_+$, find the Smarr formula, and recover the thermodynamics of a $d$-dimensional Reissner-Nordstr\"om black hole. We study the intrinsic thermodynamic stability of the shell with the chosen equations of state. We obtain that for $0<a\leq \frac{d-3}{d-2}$ all the configurations of the shell are thermodynamically stable, for $\frac{d-3}{d-2}<a<1$ stability depends on the mass and electric charge, and for $a>1$ all the configurations are unstable, except for the shell at its own gravitational radius, which is marginally stable. We rewrite the stability conditions in terms of laboratory variables. We find that the sufficient condition for the stability of these shells is when the isothermal electric susceptibility $\chi_{p,T}$ is positive, marginal stability happening when this quantity is infinite, and instability arising for configurations with a negative electric susceptibility.

Effect of a viscous fluid shell on the propagation of gravitational waves

In this paper, we show that there are circumstances in which the damping of gravitational waves (GWs) propagating through a viscous fluid can be highly significant; in particular, this applies to core collapse supernovae (CCSNe). In previous work, we used linearized perturbations on a fixed background within the Bondi-Sachs formalism to determine the effect of a dust shell on GW propagation. Here, we start with the (previously found) velocity field of the matter and use it to determine the shear tensor of the fluid flow. Then, for a viscous fluid, the energy dissipated is calculated, leading to an equation for GW damping. It is found that the damping effect agrees with previous results when the wavelength $\ensuremath{\lambda}$ is much smaller than the inner radius of the matter shell ${r}_{i}$; but, if $\ensuremath{\lambda}\ensuremath{\gg}{r}_{i}$, then the damping effect is greatly increased. Next, the paper discusses an astrophysical application, CCSNe. There are several different physical processes that generate GWs, and many models have been presented in the literature. The damping effect, thus, needs to be evaluated with each of the parameters $\ensuremath{\lambda}$ and ${r}_{i}$ and the coefficient of shear viscosity $\ensuremath{\eta}$ having a range of values. It is found that in most cases there will be significant damping and in some cases that it is almost complete. We also consider the effect of viscous damping on primordial gravitational waves generated during inflation in the early Universe. Two cases are investigated where the wavelength is either much shorter than the shell radii or much longer; we find that there are conditions that will produce significant damping, to the extent that the waves would not be detectable.

Symmetric wormholes in Einstein-vector–Gauss–Bonnet theory

We construct wormholes in Einstein-vector–Gauss–Bonnet theory where a real massless vector field is coupled to the higher curvature Gauss–Bonnet invariant. We consider three coupling functions which depend on the square of the vector field. The respective domains of existence of wormholes possess as their boundaries (i) black holes, (ii) solutions with a singular throat, (iii) solutions with a degenerate throat and (iv) solutions with cusp singularities. Depending on the coupling function wormhole solutions can feature a single throat or an equator surrounded by a double throat. The wormhole solutions need a thin shell of matter at the throat, in order to be symmetrically continued into the second asymptotically flat region. These wormhole spacetimes allow for bound and unbound particle motion as well as light rings.

Splashback Radius in a Spherical Collapse Model

It was shown several years ago that dark matter halo outskirts are characterized by very steep density profiles in a very small radial range. This feature has been interpreted as a pile-up of different particle orbits at a similar location, namely, splashback material at half an orbit after collapse. Adhikari et al. (2014) obtained the location of the splashback radius through a very simple model by calculating a dark matter shell trajectory in the secondary infall model while it crosses a growing NFW profile-shaped dark matter halo. Because they imposed a halo profile instead of calculating it from the trajectories of the shells of dark matter, they were not able to find the dark matter profile around the splashback radius. In the present paper, we use an improved spherical infall model taking into account shell crossing as well as several physical effects such as ordered and random angular momentum, dynamical friction, adiabatic contraction, etc. This allows us to determine the density profile from the inner to the outer region and to study the behavior of the outer density profile. We compare the density profiles and their logarithmic slope of with the simulation results of Diemer and Kravtsov (2014), finding a good agreement between the prediction of the model and the simulations.

Geodesic Model of HF QPOs Tested for Black Holes in Spacetimes Reflecting the Effect of Surrounding Dark Matter

Using the simple but robust model of a shell of dark matter (DM) around a Schwarzschild black hole (BH), represented by the mass ratio of the shell and BH ΔM/M, the shell extension Δr s and its inner radius r s, we study the influence of DM on the spacetime structure and geodesic motion, and provide a classification of the BH+DM shell spacetimes according to the properties of the stable circular geodesics governing Keplerian disks. We focus our attention on the epicyclic motion around circular geodesics that can be related to observational phenomena in X-ray radiation from Keplerian accretion disks, assumed to be influenced by the DM shell only gravitationally. We give the frequencies of the orbital and epicyclic motions and discuss their properties in terms of the parameters governing the DM shell. Using the frequencies in relevant variants of the standard geodesic model of high-frequency quasiperiodic oscillations (HF QPOs), we test the role of DM by fitting the HF QPO data from some microquasars and active galactic nuclei with supermassive BHs where no variant of the geodesic model applied in the standard vacuum BH background is able to explain the data. We thus provide a robust review of the applicability of the geodesic model of HF QPOs, and also provide limits on the amount of DM around a BH. We demonstrate that the geodesic model could be well applied to most observations of active galactic nuclei, with strong restrictions on the amount of invisible matter around BHs.