arXiv subjects

Andrés Aceña

Publications and source records attributed to Andrés Aceña.

15 recordsLinked to original sources

arXiv2025

Thermodynamics sheds light on the nature of dark matter galactic halos

In spherical symmetry, the gravitational potential is uniquely determined by the rotational velocity profile. Numerous galaxies exhibit a universal velocity profile from which a universal gravitational profile is inferred. When treating dark matter as either an ideal gas, a Fermi gas, or a Bose gas, only the latter can produce a gravitational profile consistent with observations, along with a temperature profile that decreases outward. This requires the mass of the boson to be below a certain threshold of $43\mbox{ eV}/c^2$. Additionally, ensuring that the speed of sound is less than the speed of light yields a lower bound on the boson's mass.

astro-ph.GA↗

arXiv2025

Spherically symmetric electrically counterpoised dust either collapses or disperses

We explore the dynamical evolution of spherically symmetric objects made of electrically counterpoised dust in general relativity. It has been claimed that these objects are in neutral equilibrium and, therefore, that black hole mimickers made of electrically counterpoised dust are feasible. Here we show that if a velocity is imparted to the fluid elements, no matter how small, the evolution leads either to a black hole or to the dispersion of the fluid. Furthermore, in the case of collapse, the resulting object is necessarily an extremal Reissner-Nordström black hole.

gr-qc↗

arXiv2024

Ruling out unitary Fermi gas of neutrinos as galactic dark matter

We investigate the possibility that galactic dark matter could be interacting fermions in the neutrino mass range. Assuming that galactic halos behave like a fluid in hydrostatic and thermal equilibrium, we employ the equation of state for a unitary Fermi gas to establish constraints on the mass of the fermion. Our findings effectively exclude neutrinos as candidates for galactic dark matter, and further reinforce earlier results suggesting that galactic dark matter is predominantly composed of light bosons.

astro-ph.GA↗

arXiv2024

Preliminary Study on Dark Matter-Dominated Systems: Further Analysis for galactic dark matter halos with Pressure

Low surface brightness galaxies are an excellent laboratory where stars and baryonic matter act as tracers of the gravitational potential of the dark matter halo. If dark matter is modeled as a perfect fluid, then spherically symmetric and static dark matter halos in hydrostatic equilibrium demand that dark matter should have an intrinsic pressure that counteracts the gravitational attraction that the dark matter halo exerts on itself. This static fluid (dark matter-dominated system, where the presence of baryons is negligible) has a specific equation of state for each rotational velocity profile of the stars in galaxies. In this work, we study the dark matter equation of state needed for the self-gravitating object to produce a gravitational potential such that the tracers follow the Universal Rotational Velocity Profile for stars of spiral galaxies proposed by Persic et al. (1996) and analyze the properties of the self-gravitating structures that emerge from this equation of state.The resulting configurations explaining the observed rotational speeds are found to be unstable. We conclude that the halo is not in hydrostatic equilibrium, it is nonspherically symmetric, or it is not static if the universal velocity profile should be valid for fitting the rotational velocity curve of the galaxies.

astro-ph.GA↗

arXiv2024

Revisiting relativistic electrically charged polytropic spheres

We revisit the problem of the structure and physical properties of electrically charged static spherically symmetric solutions of the Einstein-Maxwell system of equations where the matter model is a polytropic gas. We consider a relativistic polytrope equation of state and take the electric charge density to be proportional to the rest mass density. We construct the families of solutions corresponding to various sets of parameters and analyze their stability and compliance with the causality requirement, with special emphasis on the possibility of constructing black hole mimickers. Concretely, we want to test how much electric charge a given object can hold and how compact it can be. We conclude that there is a microscopic bound on the charge density to rest mass density ratio coincident with the macroscopic bound regarding the extremal Reissner-Nordstöm black hole. The macroscopic charge to mass ratio for the object can exceed the corresponding microscopic ratio if the object is non-extremal. Crucially, the only way to obtain a black hole mimicker is by taking a subtle limit in which an electrically counterpoised dust solution is obtained.

gr-qc↗

arXiv2023

No-go theorem for static spherically symmetric configurations composed of two charged pressureless fluid species

We present a no-go theorem for spherically symmetric configurations of two charged fluid species in equilibrium. The fluid species are assumed to be dusts, that is, perfect fluids without pressure, and the equilibrium can be attained for a single dust from the balance of electrostatic repulsion and gravitational attraction. We show that this is impossible for two dust species unless both of them are indistinguishable in terms of their electric charge density to matter density ratio. The result is obtained in the main three theories of mechanics, that is, in Newtonian Mechanics, in Special Relativity and in General Relativity. In particular, as charged dust solutions have been used to study the possibility of black hole mimickers, this result shows that such mimickers can not be constructed unless the underlying charged particle has the correct charge to mass ratio.

gr-qc↗

arXiv2023

No-go theorem for static configurations of two charged dust species

We consider static spacetimes with no specific spacial symmetry where the matter content consists of two charged dust species. This comes motivated by the fact that static configurations are possible with one dust, but only if it is electrically counterpoised dust. In order to have such dust, the quotient between electric charge density and mass density needs to be fine-tuned to a value that is far less than the charge-mass quotient for any known particle. Here we prove that there are no static configurations with two dust species unless each one is electrically counterpoised dust. This shows that electrically counterpoised dust spacetimes can not be made with matter that has on average the correct charge-mass ratio, but that the underlying particles must have such ratio.

gr-qc↗

arXiv2020

Spherically symmetric linear perturbations of electrically counterpoised dust

We consider spherically symmetric linear perturbations of static spherically symmetric spacetimes where the matter content is ellectrically counterpoised dust. We show that the evolution equation for the fluid perturbation implies that the fluid elements move with constant velocities. Therefore there are neither oscillations nor exponential departure from the background solution. We present an explicit example that shows that the perturbation could lead to the formation of a black hole.

gr-qc↗

arXiv2020

CMC surfaces and area-charge inequality for a spheroidal ECD spacetime

We consider the spacetime presented by Bonnor \cite{Bonnor98}, whose matter content is a spheroid of electrically counterpoised dust, in the context of the geometrical inequalities between area and charge. We determine numerically the constant mean curvature surfaces that are candidates to be stable isoperimetric surfaces and analyze the relation between area and charge for them, showing that a previously proved inequality is far from being saturated. We also show that the maximal initial data has a cylindrical limit where the minimum of the area-charge relation is attained.

gr-qc↗

arXiv2019

Sobolev spaces for multi-black hole initial data

In this article we introduce weighted Sobolev spaces that are well suited to treat initial data for multiple black hole systems. We prove general results for elliptic operators on these spaces and give a simple proof of existence of a class of initial data describing many extremal black holes.

gr-qc↗

arXiv2019

Circular geodesics stability in a static black hole in new massive gravity

We study the existence and stability of circular geodesics in a family of asymptotically AdS static black holes in New Massive Gravity. We show that the existence of such geodesics is determined by the sign of the hair parameter. For a positive hair parameter the stability regions follow the usual pattern, with an innermost unstable null geodesic separated from the horizon, followed by a region of unstable timelike geodesics and then stable timelike geodesics extending in the asymptotic region.

gr-qc↗

arXiv2017

Isoperimetric surfaces and area-angular momentum inequality in a rotating black hole in New Massive Gravity

We study the existence and stability of isoperimetric surfaces in a family of rotating black holes in New Massive Gravity. We show that the stability of such surfaces is determined by the sign of the hair parameter. We use the isoperimetric surfaces to find a geometric inequality between the area and the angular momentum of the black hole, conjecturing geometric inequalities for more general black holes.

gr-qc↗

arXiv2017

An Extreme Rotating Black Hole in New Massive Gravity Theory

New Massive Gravity is an alternative theory to General Relativity that is used to describe the gravitational field in a (2+1)-dimensional spacetime. Black hole solutions have been found in this theory, in particular an asymptotically anti-de Sitter rotating black hole. We analyse some features of this solution as its event horizon, black hole area and distance to the horizon, specially in the rotating extreme case, showing that they have shared features with extreme black holes in 4-dimensional General relativity. This limit case is interesting in the search of geometric inequalities as the ones found for the Kerr black hole in (3+1)-General Relativity.

gr-qc↗

arXiv2016

Extremal black hole initial data deformations

We study deformations of axially symmetric initial data for Einstein-Maxwell equations satisfying the time-rotation ($t$-$ϕ$) symmetry and containing one asymptotically cylindrical end and one asymptotically flat end. We find that the $t$-$ϕ$ symmetry implies the existence of a family of deformed data having the same horizon structure. This result allows us to measure how close solutions to Lichnerowicz equation are when arising from nearby free data.

gr-qc↗

arXiv2010

Horizon area--angular momentum inequality for a class of axially symmetric black holes

We prove an inequality between horizon area and angular momentum for a class of axially symmetric black holes. This class includes initial conditions with an isometry which leaves fixed a two-surface. These initial conditions have been extensively used in the numerical evolution of rotating black holes. They can describe highly distorted black holes, not necessarily near equilibrium. We also prove the inequality on extreme throat initial data, extending previous results.

gr-qc↗