Collapse Of Matter Research Articles

Exploring the Universe with dark light scalars

We study the cosmology of the dark sector consisting of (ultra)light scalars. Since the scalar mass is radiatively unstable, a special explanation is required to make the mass much smaller than the UV scale. There are two well-known mechanisms for the origin of scalar mass. The scalar can be identified as a pseudo-Goldstone boson, whose shift symmetry is explicitly broken by nonperturbative corrections, like the axion. Alternatively, it can be identified as a composite particle like the glueball, whose mass is limited by the confinement scale of the theory because no scalar degree of freedom exists at high scales. In both cases, the scalar can be naturally light, but interaction behavior is quite different. The lighter the axion (glueball), the weaker (stronger) its interaction. As the simplest nontrivial example, we consider the dark axion whose shift symmetry is anomalously broken by the hidden non-Abelian gauge symmetry. After the confinement of the gauge group, the dark axion and the dark glueball get masses and both form multicomponent dark matter. We carefully consider the effects of energy flow from the dark gluons to the dark axions and derive the full equations of motion for the background and the perturbed variables. The effect of the dark axion--dark gluon coupling on the evolution of the entropy and the isocurvature perturbations is also clarified. Finally, we discuss the gravothermal collapse of the glueball subcomponent dark matter after the halos form, in order to explore the potential to contribute to the formation of seeds for the supermassive black holes observed at high redshifts. With the simplified assumptions, the glueball subcomponent dark matter with the mass of 0.01--0.1 MeV and the axion main dark matter component with the decay constant ${f}_{a}=\mathcal{O}({10}^{15}--{10}^{16})\text{ }\text{ }\mathrm{GeV}$ and the mass of $\mathcal{O}({10}^{\ensuremath{-}14}--{10}^{\ensuremath{-}18})\text{ }\text{ }\mathrm{eV}$ can provide a hint on the origin of the supermassive black holes at high redshifts.

The threehundred: the structure and properties of cosmic filaments in the outskirts of galaxy clusters

ABSTRACT Galaxy cluster outskirts are described by complex velocity fields induced by diffuse material collapsing towards filaments, gas, and galaxies falling into clusters, and gas shock processes triggered by substructures. A simple scenario that describes the large-scale tidal fields of the cosmic web is not able to fully account for this variety, nor for the differences between gas and collisionless dark matter. We have studied the filamentary structure in zoom-in resimulations centred on 324 clusters from the threehundred project, focusing on differences between dark and baryonic matter. This paper describes the properties of filaments around clusters out to five R200, based on the diffuse filament medium where haloes had been removed. For this, we stack the remaining particles of all simulated volumes to calculate the average profiles of dark matter and gas filaments. We find that filaments increase their thickness closer to nodes and detect signatures of gas turbulence at a distance of ${\sim}2 \rm {{{~h^{-1}\,{\rm Mpc}}}}$ from the cluster. These are absent in dark matter. Both gas and dark matter collapse towards filament spines at a rate of ${\sim}200 \,\rm {km ~ s^{-1}\, h^{-1}}$. We see that gas preferentially enters the cluster as part of filaments, and leaves the cluster centre outside filaments. We further see evidence for an accretion shock just outside the cluster. For dark matter, this preference is less obvious. We argue that this difference is related to the turbulent environment. This indicates that filaments act as highways to fuel the inner regions of clusters with gas and galaxies.

Photon spectrum of asymmetric dark stars

Asymmetric Dark Stars, i.e. compact objects formed from the collapse of asymmetric dark matter could potentially produce a detectable photon flux if dark matter particles self-interact via dark photons that kinetically mix with ordinary photons. The morphology of the emitted spectrum is significantly different and therefore distinguishable from a typical black-body one. Given the above and the fact that asymmetric dark stars can have masses outside the range of neutron stars, the detection of such a spectrum can be considered as a smoking gun signature for the existence of these exotic stars.

Stirred and shaken: Dynamical behavior of boson stars and dark matter cores

Bosonic fields can give rise to self-gravitating structures. These are interesting hypothetical new “dark matter stars” and good descriptions of dark matter haloes if the fields are very light. We study the dynamical response of Newtonian boson stars (NBS) when excited by external matter (stars, planets or black holes) in their vicinities. Our setup can describe the interaction between a massive black hole and the surrounding environment, shortly after the massive body has undergone a “kick”, due to the collapse of baryonic matter at the galactic center, or dark matter depletion as a reaction to an inspiralling binary. We perform the first self-consistent calculation of dynamical friction acting on moving bodies in these backgrounds. Binaries close to coalescence “stir” the NBS core, and backreaction affects gravitational waveforms at leading −6PN order with respect to the dominant quadrupolar term; the coefficient is too small to allow detection by next-generation interferometers. We also show that the gravitational collapse to a supermassive black hole at the center of a NBS is accompanied by only a small change in the surrounding core. The NBS eventually gets accreted, but for astrophysical parameters this occurs only after several Hubble times.

Response of ultralight dark matter to supermassive black holes and binaries

Scalar fields can give rise to confined structures, such as boson stars or Q-balls. These objects are interesting hypothetical new "dark matter stars," but also good descriptions of dark matter haloes when the fields are ultralight. Here, we study the dynamical response of such confined bosonic structures when excited by external matter (stars, planets or black holes) in their vicinities. Such perturbers can either be plunging through the bosonic configuration or simply act as periodic sources. Our setup can also efficiently describe the interaction between a massive black hole and the surrounding environment, shortly after the massive body has undergone a "kick", due to the collapse of baryonic matter at the galactic center. It also depicts dark matter depletion as a reaction to an inspiralling binary within the halo. We calculate total energy loss, and linear and angular momenta radiated during these processes, and perform the first self-consistent calculation of dynamical friction acting on moving bodies in these backgrounds. We show that the gravitational collapse to a supermassive black hole at the center of a Newtonian boson star (NBS) is accompanied by a small change in the surrounding core. The NBS eventually gets accreted, but only on times larger than a Hubble scale for astrophysical parameters. Stellar or supermassive binaries are able to "stir" and expel scalar from the NBS. For binaries in the LIGO or LISA band, close to coalescence, scalar emission affects the waveform at leading $-6$ PN order with respect to the dominant quadrupolar term; the coefficient is too small to allow detection by next-generation interferometers. Our results provide a complete picture of the interaction between black holes or stars and the ultralight dark matter environment they live in.

Towards consistent black-to-white hole bounces from matter collapse

This article presents a new model-independent constraint for bouncing black hole geometries. This constraint, applicable for a physical black hole formed by a collapsing compact object, sets a bound on the minimal allowed radius of the time-like surface of the collapsing star at the bounce. It follows from this bound that the shell always bounces in an untrapped region or precisely on a trapping horizon. This constraint is of purely kinematical origin as it descends from the continuity of the metric between the geometries describing the interior and exterior of the collapsing object so that it is completely model-independent. The second part of this work investigates the conditions under which an effective extension of the Oppenheimer-Snyder collapse can describe consistent black-to-white hole bounces. Therefore, we present a general framework in which the collapse can lead to the formation of outer and inner horizons. We show that on top of the previous kinematical constraint, an additional dynamical condition has to be satisfied in order for the model to admit well-defined black-to-white hole solutions. As expected, this second condition turns out to be model-dependent. The resulting class of models describing bouncing compact objects are characterized by three parameters for the star (mass, initial radius and density) and two quantum parameters descending from the UV-completion of the exterior and interior geometries. The solution space contains (1) bouncing stars and (2) bouncing black holes and (3) a new class of astrophysical objects which alternate between a bouncing star and a bouncing black hole. Finally, we provide an explicit construction of a black-to-white hole bounce using the techniques of spatially closed LQC and discuss the novel properties induced by the presence of the inner horizon in this new framework. This generic framework lays down the foundation for interesting phenomenological investigations concerning the astrophysical properties of these objects, as well as a novel platform for further developments.

On dynamic aspects of the Proca field screening by a black hole

Classical black holes are known for almost half a century to nullify exterior classical massive vector field associated with a charge crossing the event horizon. This implies that, from the point of view of an external observer, the Proca field of the charge is screened with the strength gradually increasing as the charge adiabatically approaches the event horizon. In this paper we reject the adiabaticity constraint and calculate analytically the field evolution with respect to a distant observer in the frame of the simplest model of a contracting charged spherical shell concentrically surrounding a Schwarzschild black hole. We show that a time scale of the screening is determined by a mass of the black hole and, moreover, loss of Proca hair during the collapse of charged matter has the same temporal character. Due to existence of the event horizon, there is discontinuous jump between massive and massless electrodynamics. This means that presence of an arbitrarily small mass of the photon induces observable effects, which include generation of electric asymmetry of the Universe and galactic magnetic fields.

Effect of heating on some soil properties and potassium dynamics in calcareous soils of southern Iran

AbstractPrescribed burning of plant residues in agricultural lands may increase surface soil temperature and change the dynamics of soil potassium (K). In the current investigation, the effects of two hours heating of soil to 25, 100, 225, or 350°C and cycling (one and three cycles) on properties of eight calcareous soils from southern Iran and K dynamics (K forms, release, and fixation) were studied. Results indicated that heating to 100 or 225°C had no significant effect on pH,EC, or CEC but heating to 350°C increased soil EC (from 0.53 to 0.66 dS m−1) and decreased CEC (from 25 to 19 cmol kg−1). The heating to 350°C increased all forms of K including soluble (from 36 to 84 mg kg−1, 133% increase), exchangeable (from 285 to 490 mg kg−1), non‐exchangeable (from 598 to 686 mg kg−1), and HNO3‐extractable (from 922 to 1260 mg kg−1) decreased K fixation capacity of all soils (from 351 to 235 mg kg−1). Cumulative K release from soils to 0.025 M CaCl2 ranged from 114 to 438 mg kg−1 and increased significantly after heating of soils to 350°C and reached between 233 and 783 mg kg−1. Potassium fixation capacity of fine‐textured soils (soils 2, 6, 7, and 8) after 10 times extraction with CaCl2 was increased (65%–190%). Generally, heating of soils to 350°C caused combustion of organic matter and partial destruction or collapse of K‐bearing minerals and increased release of K.

Bouncing compact objects. Part I. Quantum extension of the Oppenheimer-Snyder collapse

This article proposes a generalization of the Oppenheimer-Snyder model which describes a bouncing compact object. The corrections responsible for the bounce are parameterized in a general way so as to remain agnostic about the specific mechanism of singularity resolution at play. It thus develops an effective theory based on a thin shell approach, inferring generic properties of such a UV complete gravitational collapse. The main result comes in the form of a strong constraint applicable to general UV models: if the dynamics of the collapsing star exhibits a bounce, it always occurs below, or at most at the energy threshold of horizon formation, so that only an instantaneous trapping horizon may be formed while a trapped region never forms. This conclusion relies solely on i) the assumption of continuity of the induced metric across the time-like surface of the star and ii) the assumption of a classical Schwarzschild geometry describing the (vacuum) exterior of the star. In particular, it is completely independent of the choice of corrections inside the star which leads to singularity-resolution. The present model provides thus a general framework to discuss bouncing compact objects, for which the interior geometry is modeled either by a classical or a quantum bounce. In the latter case, our no-go result regarding the formation of trapped region suggests that additional structure, such as the formation of an inner horizon, is needed to build consistent models of matter collapse describing black-to-white hole bounces. Indeed, such additional structure is needed to keep quantum gravity effects confined to the high curvature regime, in the deep interior region, providing thus a new challenge for current constructions of quantum black-to-white hole bounce models.

Critical phenomena in gravitational collapse with two competing massless matter fields

In the gravitational collapse of matter beyond spherical symmetry, gravitational waves are necessarily present. On the other hand, gravitational waves can collapse to a black hole even without matter. One might therefore wonder whether the interaction and competition between the matter fields and gravitational waves affects critical phenomena at the threshold of black hole formation. As a toy model for this, we study type II critical collapse with two matter fields in spherical symmetry, namely a scalar field and a Yang-Mills field. On their own, both display discrete self-similarity (DSS) in type II critical collapse, and we can take either one of them as a toy model for gravitational waves. To our surprise, in numerical time evolutions we find that, for sufficiently good fine-tuning, the scalar field always dominates on sufficiently small scales. We explain our results by the conjectured existence of a "quasi-discretely self-similar" (QSS) solution shared by the two fields, equal to the known Yang-Mills critical solution at infinitely large scales and the known scalar field critical solution (the Choptuik solution) at infinitely small scales, with a gradual transition from one field to the other. This QSS solution itself has only one unstable mode, and so acts as the critical solution for any mixture of scalar field and Yang-Mills initial data.

Accretion-induced Collapse of Dark Matter Admixed White Dwarfs. II. Rotation and Gravitational-wave Signals

Abstract We present axisymmetric hydrodynamical simulations of accretion-induced collapse (AIC) of dark matter (DM) admixed rotating white dwarfs (WD) and their burst gravitational-wave (GW) signals. For initial WD models with the same central baryon density, the admixed DM is found to delay the plunge and bounce phases of AIC, and decrease the central density and mass of the protoneutron star (PNS) produced. The bounce time, central density, and PNS mass generally depend on two parameters, the admixed DM mass M DM and the ratio between the rotational kinetic and gravitational energies of the inner core at bounce . The emitted GWs have generic waveform shapes and the variation of their amplitudes h + show a degeneracy on and M DM. We found that the ratios between the GW amplitude peaks around bounce allow breaking of the degeneracy and extraction of both and M DM. Even within the uncertainties of the nuclear matter equation of state, a DM core can be inferred if its mass is greater than 0.03 M ⊙. We also discuss possible DM effects on the GW signals emitted by PNS g-mode oscillations. GWs may boost the possibility for the detection of AIC, as well as open a new window into the indirect detection of DM.

Using kinetic theory to examine a self-gravitating system composed of baryons and cold dark matter

We examine the evolution of non-relativistic cold dark matter gravitationally coupled to baryons with modes deep inside the Hubble radius (sub-horizon regime) using a kinetic theory approach within the realm of Newtonian theory. We obtain the general solution for the total density perturbation and we also show that a baryon perturbation catches up with the dark matter perturbation at late times, which in turn makes possible the formation of bound structures. We extend the linear perturbation analysis by considering the turn-around event, collapse of matter, and its virialization process.

Gravitational collapse of baryonic and dark matter

A massive star undergoes a continual gravitational collapse when the pressures inside the collapsing star become insufficient to balance the pull of gravity. The Physics of gravitational collapse of stars is well studied. Using general relativistic techniques, one can show that the final fate of such a catastrophic collapse can be a black hole or a naked singularity, depending on the initial conditions of gravitational collapse. While stars are made of baryonic matter whose collapse is well studied, there is good indirect evidence that another type of matter, known as dark matter, plays an important role in the formation of large-scale structures in the universe, such as galaxies. It is estimated that some 85% of the total matter in the universe is dark matter. Since the particle constituent of dark matter is not known yet, the gravitational collapse of dark matter is less explored. Here, we consider first some basic properties of baryonic matter and dark matter collapse. Then, we discuss the final fate of gravitational collapse for different types of matter fields and the nature of the singularity which can be formed as an endstate of gravitational collapse. We then present a general relativistic technique to form equilibrium configurations, and argue that this can be thought of as a general relativistic analog of the standard virialization process. We suggest a modification, where the top-hat collapse model of primordial dark-matter halo formation is modified using the general relativistic technique of equilibrium. We also explain why this type of collapse process is more likely to happen in the dark-matter fields.

Spherical collapse of fuzzy dark matter

It has been postulated that Fuzzy Dark Matter (FDM) could be a viable alternative to Cold Dark Matter (CDM). FDM is comprised of ultralight bosons which exist as a Bose-Einstein condensate. Due to the very low mass of FDM, the de Broglie wavelength of these bosons are of the order of kpc and the quantum effects manifest at those scales. Hence, unlike CDM, FDM experiences quantum pressure along with gravitational attraction. In this work, we investigate the gravitational collapse of a spherically symmetric FDM overdensity. We assume a power law density profile for an overdense region of FDM and derive an expression for the temporal evolution of a spherical shell in the non-interacting limit and use it to derive an expression for average overdensity contained in the spherical shell in an Einstein--de Sitter universe. Further, we numerically extend the analysis to the case of interacting bosons. Finally, we discuss the virialization of such an overdense region of non-interacting FDM and derive an expression for overdensity in the linear and the full theory. We compare our results with those obtained in the case of CDM and conclude with a discussion of the results.

Quasi-spherical collapse of matter in ΛCDM

We report the findings of new exact analytical solutions to the cosmological fluid equations, namely for the case where the initial conditions are perturbatively close to a spherical top-hat profile. To do so we enable a fluid description in a Lagrangian-coordinates approach, and prove the convergence of the Taylor-series representation of the Lagrangian displacement field until the time of collapse ("shell-crossing"). This allows the determination of the time for quasi-spherical collapse, which is shown to happen generically earlier than in the spherical case. For pedagogical reasons, calculations are first given for a spatially flat universe that is only filled with a non-relativistic component of cold dark matter (CDM). Then, the methodology is updated to a $\Lambda$CDM Universe, with the inclusion of a cosmological constant $\Lambda>0$.

The Radiological Imaging Features of Easily Misdiagnosed Epithelioid Glioblastoma in Seven Patients

We review the radiological imaging features and report histopathological findings of 7 adult patients with epithelioid glioblastoma (eGBM), which was a newly revised subtype of glioblastoma. Seven adult patients with a diagnosis of eGBM on a brain tissue specimen were retrospectively confirmed by pathology. The tumor magnetic resonance imaging characteristics such as location, number, edema, necrosis, hemorrhage, enhancement, diffusion-weighted image, apparent diffusion coefficient, magnetic resonance spectroscopy, dynamic susceptibility contrast-perfusion-weighted imaging, and histopathological findings were documented. The tumors of these patients exhibited iso-hyperintensive signal on the T2-weighted image and iso-hypointensive signal on the T1-weighted image. All the lesions manifested iso-hypointensive signal on the diffusion-weighted image, and 2 cases showed significantly restricted hyperintensive signal (2/7). Peritumoral edema in all cases was mild. Five cases were located in the cortical lobe (5/7) and the other 2 were multifocal (2/7). Four cases showed white matter collapse sign (4/7). These tumors revealed apparent enhancement after contrast injection. In particular, 4 cases displayed capsuled sign (4/7), 2 cases showed dura mater tail sign (2/7), and 1 case showed hemorrhage (1/7). The mean value of apparent diffusion coefficient in 6 cases was 1.09× 10-3 mm2/s. The mean value of relative cerebral blood volume in 3 cases was 2.84× 10-3 mm2/s on dynamic susceptibility contrast-perfusion-weighted imaging. The average value of the choline/N-acetyl aspartate ratio in 4 cases was 6.47× 10-3 mm2/s on magnetic resonance spectroscopy. All cases expressed a BRAF V600E mutation according to molecular characteristics. eGBMs that were predominantly located in cortex with mild peritumoral edema, white matter collapse, encapsular sign, and dura mater tail sign could be easily misdiagnosed as cortex-involved intracranial brain tumor such as meningioma, whereas multifocal tumors could be easily misdiagnosed as metastatic tumor and lymphoma. Multimodal images were helpful for the differential diagnosis.

Dynamo effects in gravity

Nonlinear oscillations in the dynamic system of gravitational and material fields are considered. The problems of singularities and caustics in gravity, expansion and baryon asymmetry of the Universe, wave prohibition of collapse into black holes, and failure of the Big Bang concept are discussed. It is assumed that the effects of the expansion of the Universe are coupling with the reverse collapse of dark matter. This hypothesis is used to substantiate the vortex and fractal structures in the distribution of matter. A system of equations is proposed for describing turbulent and fluctuation processes in gravitational and material fields. Estimates of the di usion parameters of such a system are made in comparison with the gravitational constant.

Relativistic collapse of axion stars

We study the gravitational collapse of axion dark matter in null coordinates, assuming spherical symmetry. Compared with previous studies, we use a simpler numerical scheme which can run, for relevant parameters, in a few minutes or less on a desktop computer. We use it to accurately determine the domains of parameter space in which the axion field forms a black hole, an axion star or a relativistic Bosenova.

Pre-Hawking radiation cannot prevent the formation of apparent horizon

As an attempt to solve the black hole information loss paradox, recently there has been the suggestion that, due to semiclassical effects, a pre-Hawking radiation must exist during the gravitational collapse of matter, which in turn prevents the apparent horizon from forming. Assuming the pre-Hawking radiation does exist, here we argue the opposite. First we note that the stress energy tensor near the horizon for the pre-Hawking radiation is far too small to do anything to the motion of a collapsing shell. Thus the shell will always cross the apparent horizon within a finite proper time. Moreover, the amount of energy that can be radiated must be less than half of the total initial energy (if the particle starts at rest at infinity) before the shell becomes a null shell and cannot radiate any more without becoming tachyonic. We conclude that for any gravitational collapsing process within Einstein gravity and semiclassical quantum field theory, the formation of the apparent horizon is inevitable. Pre-Hawking radiation is therefore not a valid solution to the information paradox.

Decay as a black metal symbol

Abstract This article intends to dissect black metal’s interestingly twisted relationship with decay. A deep study encompassing symbols of atrophy, with the eventual intention of observing and analysing them through a kaleidoscope of philosophical thought, influenced by, amongst others, the musings of Bataille, Kant and Nietzsche. Issues appearing in both the real and the metaphorical will be placed under inspection, and a suitably blackened light will be shone towards the extent of how black metal exists and thrives in the organic collapse of matter and sound. There will be discussions on how black metal has itself become attuned to decay and how the two processes feed off each other, exist in harmonic conjunction and on rare occasions, oppose the other’s being. How black metal has metastasized with atrophy. Here we shall see two forces inexplicably intertwined, the numerous links given exposure and attempted understanding in the realm of black metal theory.