Jose Domingo Arbanil Vela
@upn.edu.pe
Universidad Privada del Norte
RESEARCH, TEACHING, or OTHER INTERESTS
Physics and Astronomy, General Physics and Astronomy, Astronomy and Astrophysics
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
César V. Flores, C. H. Lenzi, M. Dutra, O. Lourenço, and José D. V. Arbañil
American Physical Society (APS)
Juan M.Z. Pretel, Sergio E. Jorás, Ribamar R.R. Reis, Sergio B. Duarte, and José D.V. Arbañil
Elsevier BV
José D. V. Arbañil, Cesar V. Flores, César H. Lenzi, and Juan M. Z. Pretel
American Physical Society (APS)
The effects of the anisotropy on the fluid pulsation modes adopting the so-called Cowling approximation and tidal deformability of strange quark stars are investigated by using the numerical integration of the hydrostatic equilibrium, nonradial oscillations, and tidal deformability equations, being these equations modified from their standard form to include the anisotropic effects. The fluid matter inside the compact stars is described by the MIT bag model equation of state. For the anisotropy profile, we consider a local anisotropy that is both regular at the center and null at the star's surface. We find that the effect of the anisotropy is reflected in the fluid pulsation modes and tidal deformability. Finally, we analyze the correlation between the tidal deformability of the GW$170817$ event with the anisotropy.
José D. V. Arbañil, Lucas S. Rodrigues, and César H. Lenzi
Springer Science and Business Media LLC
AbstractIn this work, we investigate the influence of the phase transition and a stiffer fluid in neutron stars’ cores on the static equilibrium configuration, dynamical stability, and tidal deformability. For this aim, it is taken into account that the fluid in the core and the envelope follow the relativistic polytropic equation of state. We find that the phase transition and a stiffer fluid in the core will reflect in the total mass, radius, speed of sound, core radius, radial stability with a slow and rapid conversion at the interface, and tidal deformability. We also investigate the dimensionless tidal deformability $$\\varLambda _1$$ Λ 1 and $$\\varLambda _2$$ Λ 2 for a binary neutron stars system with chirp mass equal to GW170817. Finally, we contrast our results with observational data to show the role that phase transition and a stiffer core fluid could play in the study of neutron stars.
Juan M.Z. Pretel, José D.V. Arbañil, Sergio B. Duarte, Sergio E. Jorás, and Ribamar R.R. Reis
IOP Publishing
Abstract We provide the modified TOV equations for the hydrostatic equilibrium of charged compact stars within the metric f(R) gravitational background. We adopt the MIT bag model EoS for the dense matter and assume a charge distribution where the electric charge density ρ ch is proportional to the standard energy density ρ. Using the Starobinsky model, we explore the role of the αR 2 term, where α is a free constant and R the Ricci scalar, on the global properties of charged stars such as radius, mass and total charge. We present the dependence of the structure of the star for several values of α and for different values of the constant parameter β ≡ ρ ch/ρ. Remarkably, we find that the radius decreases with respect to its GR value for low central densities, while the opposite occurs in the high-central-density region. The mass measured at the surface always decreases and the maximum-total charge undergoes a substantial increase as the parameter α increases. We also illustrate the variations of the asymptotic mass as a consequence of the electric charge and the extra quadratic term.
José D. V. Arbañil and Grigoris Panotopoulos
American Physical Society (APS)
José D. V. Arbañil 2, ∗ and Grigoris Panotopoulos 4, † Facultad de Ciencias F́ısicas, Universidad Nacional Mayor de San Marcos, Avenida Venezuela s/n Cercado de Lima, 15081 Lima, Peru Departamento de Ciencias, Universidad Privada del Norte, Avenida el Sol 461 San Juan de Lurigancho, 15434 Lima, Peru Centro de Astrof́ısica e Gravitação-CENTRA, Departamento de F́ısica, Instituto Superior Técnico-IST, Universidade de Lisboa-UL, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal Departamento de Ciencias F́ısicas, Universidad de la Frontera, Casilla 54-D, 4811186 Temuco, Chile (Dated: December 21, 2021)
J D V Arbañil, C H Lenzi, and M Malheiro
IOP Publishing
Abstract The influence of the dimensions on the f and p 1 pulsation modes from strange quark stars, in the Cowling approximation, are investigated. For that purpose, the d-dimensional nonradial pulsation equations (d > 4) are numerically integrated considering that the Schwarzschild-Tangherlini line element describes the spacetime outside the object. We found that the fluid pulsation modes could become larger than those obtained in four dimensions. In four dimensions, the f pulsation mode is nearly constant, and for high total masses, it increases monotonically and quickly with the total mass. In this mass interval, the f frequencies grow for the spacetime dimensions between 4 and 6 and decay for d larger than 7. Concerning the p 1 pulsation modes, we found that they increase with the spacetime dimension and decline with the increment of the total mass.
Sílvia P. Nunes, José D. V. Arbañil, and Manuel Malheiro
American Astronomical Society
We investigate the structure and stability against radial oscillations, pycnonuclear reactions, and inverse β-decay of hot white dwarfs. We consider the fluid matter to be made up of nucleons and electrons confined in a Wigner–Seitz cell surrounded by free photons. It is considered that the temperature depends on the mass density considering the presence of an isothermal core. We find that the temperature produces remarkable effects on the equilibrium and radial stability of white dwarfs. The stable equilibrium configuration results are compared with those for white dwarfs estimated from the Extreme Ultraviolet Explorer survey and the Sloan Digital Sky Survey. We derive masses, radii, and central temperatures for the most massive white dwarfs according to the surface gravity and effective temperature reported by the surveys. We note that these massive stars are in the mass region where general relativity effects are important. These stars are near the threshold of instabilities due to radial oscillations, pycnonuclear reactions, and inverse β-decay. Regarding the radial stability of these stars as a function of the temperature, we find that it decreases with the increment of central temperature. We also find that the maximum-mass point and the zero eigenfrequencies of the fundamental mode are determined at the same central energy density. Regarding low-temperature stars, pycnonuclear reactions occur in similar central energy densities, and the central energy density threshold for inverse β-decay is not modified. For T c ≥ 1.0 × 108 [K], the onset of radial instability is attained before pycnonuclear reaction and inverse β-decay.
Juan M.Z. Pretel, Sergio E. Jorás, Ribamar R.R. Reis, and José D.V. Arbañil
IOP Publishing
Abstract We investigate the equilibrium and radial stability of spherically symmetric relativistic stars, considering a polytropic equation of state (EoS), within the framework of f(R,T) gravity with a conservative energy-momentum tensor. Both modified stellar structure equations and Chandrasekhar's pulsation equations are derived for the f(R,T)= R+ h(T) gravity model, where the function h(T) assumes a specific form in order to safeguard the conservation equation for the energy-momentum tensor. The neutron star properties, such as radius, mass, binding energy and oscillation spectrum are studied in detail. Our results show that a cusp — which signals the appearance of instability — is formed when the binding energy is plotted as a function of the compact star proper mass. We find that the squared frequency of the fundamental vibration mode passes through zero at the central-density value corresponding to such a cusp where the binding energy is a minimum.
Juan M.Z. Pretel, Sergio E. Jorás, Ribamar R.R. Reis, and José D.V. Arbañil
IOP Publishing
Abstract We examine the static structure configurations and radial stability of compact stars within the context of f(R, T) gravity, with R and T standing for the Ricci scalar and trace of the energy-momentum tensor, respectively. Considering the f(R, T)=R+2β T functional form, with β being a constant, we derive the corresponding hydrostatic equilibrium equation and the modified Chandrasekhar's pulsation equation. The mass-radius relations and radial mode frequencies are obtained for some realistic equations of state. Our results show that the traditional stellar stability criteria, namely, the necessary condition d M/dρc >0 and sufficient condition ω2 >0, still hold in this theory of gravity.
José D. V. Arbañil, César H. Lenzi, and Manuel Malheiro
American Physical Society (APS)
In this work, we make the first step to derive non-radial pulsation equations in extra dimensions and investigate how the $f$- and $p_1$-mode frequencies of strange quark stars, within the Cowling approximation, change with the number of dimensions. In this regard, the study is performed by solving numerically the non-radial pulsation equations, adjusted for a $d$-dimensional space-time $(d\\geq4)$. We connect the interior to a Schwarzschild-Tangherlini exterior metric and analyze the $f$- and $p_1$- mode frequencies. We found that the frequencies could become higher than those found in four-dimensional space-time. The $f$-mode frequency is essentially constant and only for large gravitational radius values grows monotonically and fast with the gravitational radius. In a gravitational radius range, where $f$-mode frequencies are constant, they increase for space-time dimensions $4\\leq d\\leq6$ and decrease for $d\\geq7$. Regarding $p_1$-mode frequencies they are always larger for higher dimensions and decay monotonically with the increase of the gravitational radius. In extra dimensions, as it happens for four-dimensional space-time, we found $p_1$-mode frequencies are always larger than the $f$-modes ones. In the Newtonian gravity, for a homogeneous star in $d$ dimensions, we observe that the $f$-mode eigenfrequencies are constant and given by the relation $\\omega^2=l\\, M\\, G_d/R^{d-1}$; where $l$ represents the spherical harmonic index, $M\\,G_d$ being the total star mass and $R$ the stellar radius.
José D. V. Arbañil and Manuel Malheiro
IOP Publishing
Abstract The influence of the extra dimensions on the equilibrium and radial pulsation of a compact object is investigated. For such purpose, we solve the stellar structure equations and radial pulsation equations, both modified from their original version to include the extra dimensions (d ≥ 4) taking into account that spacetime outside the object is depicted by a Schwarzschild-Tangherlini metric. In addition, we consider that the pressure and the energy density are connected by a linear relation. Some properties of compact objects are analyzed, such as mass and period of the fundamental mode and their dependencies with the spacetime dimensions. We found that the maximum mass marks the begining of the instability, indicating that in a sequence of equilibrium configurations, the regions constitute by stable and unstable compact objects are distinguished by the relations d M / d ρ c d > 0 and d M / d ρ c d < 0 , respectively.
José D. V. Arbañil and Pedro H. R. S. Moraes
Springer Science and Business Media LLC
José D V Arbañil, Pedro H R S Moraes, and Manuel Malheiro
IOP Publishing
In this work we derive a gravastar model in Randall–Sundrum II braneworld scenario. Gravastars (or gravitationally vacuum stars) were proposed by Mazur and Mottola as systems of gravitational collapse alternative to black holes. The external region of the gravastar is described by a Schwarzschild space-time, while its internal region is filled by dark energy. In between there is a thin shell surface with ultrarelativistic matter (sometimes referred to as stiff matter). We obtain solutions for some physical quantities of the braneworld gravastars. Those are compared to original Mazur–Mottola results as well as with some gravastar solutions in alternative gravity theories. The consequences of the braneworld setup in gravastar physics is deeply discussed.
José D. V. Arbañil, Geanderson A. Carvalho, Ronaldo V. Lobato, Rubens M. Marinho, and Manuel Malheiro
American Physical Society (APS)
We analyze the influence of extra dimensions on the static equilibrium configurations and stability against radial perturbations. For this purpose, we solve stellar structure equations and radial perturbation equations, both modified for a $d$-dimensional spacetime ($d\\geq4$) considering that spacetime outside the object is described by a Schwarzschild-Tangherlini metric. These equations are integrated considering a MIT bag model equation of state extended for $d\\geq4$. We show that the spacetime dimension influences both the structure and stability of compact objects. For an interval of central energy densities $\\rho_{cd}\\,G_d$ and total masses $MG_d/(d-3)$, we show that the stars gain more stability when the dimension is increased. In addition, the maximum value of $M{G_d}/(d-3)$ and the zero eigenfrequency of oscillation are found with the same value of $\\rho_{cd}\\,G_d$; i.e., the peak value of $M{G_d}/(d-3)$ marks the onset of instability. This indicates that the necessary and sufficient conditions to recognize regions constructed by stable and unstable equilibrium configurations against radial perturbations are, respectively, $dM/d\\rho_{cd}>0$ and $dM/d\\rho_{cd}<0$. We obtain that some physical parameter of the compact object in a $d$-dimensional spacetime, such as the radius and the mass, depend of the normalization. Finally, within the Newtonian framework, the results show that compact objects with adiabatic index $\\Gamma_1\\geq2(d-2)/(d-1)$ are stable against small radial perturbations.
José D. V. Arbañil and Vilson T. Zanchin
American Physical Society (APS)
We study the static stellar equilibrium configurations ofuncharged and charged spheres composed by a relativistic polytropic fluid, and compare with those of spheres composed by a non-relativistic polytropic fluid, the later case already being studied in a previous work [J. D. Arba\\~nil, P. S. Lemos, V. T. Zanchin, Phys. Rev. D \\textbf{88}, 084023 (2013)]. In the relativistic fluid case, a relativistic polytropic equation of state, $p=\\omega\\delta^{\\gamma}$, is assumedd. Here, $\\delta=\\rho-p/(\\gamma-1)$, with $\\delta$ and $\\rho$ being the rest mass density and the energy density, respectively, and $\\omega$ and $\\gamma$ are respectively the polytropic constant and the polytropic exponent. We assume that the charge density $\\rho_e$ is proportional to the energy density $\\rho$, $\\rho_e = \\alpha\\, \\rho$, with $\\alpha$ being a constant such that $0\\leq |\\alpha|\\leq 1$. Some properties of the charged spheres such as mass, total electric charge, radius, redshift, and the speed of sound are analyzed. The dependence of such properties with the polytropic exponent is also investigated. In addition, some limits that arise in general relativity, such as the Chandrasekhar limit, the Oppenheimer-Volkoff limit, the Buchdahl bound and the Buchdahl-Andr\\'easson bound, i.e., the Buchdahl bound for the electric case, are studied. As in a charged non-relativistic polytropic sphere, the charged relativistic polytropic sphere with $\\gamma\\to\\infty$ and $\\alpha \\to 1$ saturates the Buchdahl-Andr\\'easson bound, thus indicating that it reaches the quasiblack hole configuration. We show by means of numerical analysis that, as expected, the major differences between the two cases appear in the high energy density region.
G. A. Carvalho, José D. V. Arbañil, R. M. Marinho, and M. Malheiro
Springer Science and Business Media LLC
José D. V. Arbañil and Manuel Malheiro
WORLD SCIENTIFIC
G. A. Carvalho, R. V. Lobato, P. H. R. S. Moraes, José D. V. Arbañil, E. Otoniel, R. M. Marinho, and M. Malheiro
Springer Science and Business Media LLC
Germán Lugones and José D V Arbañil
IOP Publishing
The properties of spherically symmetric static compact stars are studied in the Randall-Sundrum II type braneworld model assuming that the spacetime outside the star is described by a Schwarzschild metric. The integration of the stellar structure equations employing the so called causal limit equation of state (EoS) shows that the equilibrium solutions can violate the general relativistic causal limit. An analysis of the properties of hadronic and strange quark stars using standard EoSs confirm the same result: there is a branch in the mass-radius diagram that shows the typical behaviour found within the frame of General Relativity and another branch of stars that are supported against collapse by the nonlocal effects of the bulk on the brane. Stars belonging to the new branch can violate the general relativistic causal limit, may have an arbitrarily large mass, and are stable under small radial perturbations. If they exist in Nature, these objects could be hidden among the population of black hole candidates. The future observation of compact stars with masses and radii falling above the causal limit of General Relativity but below the Schwarzschild limit maybe a promising astrophysical evidence for the existence of extra dimensions.
Germán Lugones and José D. V. Arbañil
American Physical Society (APS)
We study the properties of compact stars in the Randall-Sundrum II type braneworld model. To this end, we solve the braneworld generalization of the stellar structure equations for a static fluid distribution with spherical symmetry considering that the spacetime outside the star is described by a Schwarzschild metric. First, the stellar structure equations are integrated employing the so called causal limit equation of state (EOS), which is constructed using a well established EOS at densities below a fiducial density, and the causal EOS $P= \\rho$ above it. It is a standard procedure in general relativistic stellar structure calculations to use such EOS for obtaining a limit in the mass radius diagram, known as causal limit, above which no stellar configurations are possible if the EOS fulfills that the sound velocity is smaller than the speed of light. We find that the equilibrium solutions in the braneworld model can violate the general relativistic causal limit and, for sufficiently large mass they approach asymptotically to the Schwarzschild limit $M = 2 R$. Then, we investigate the properties of hadronic and strange quark stars using two typical EOSs. For masses below $\\sim 1.5 - 2 M_{\\odot}$, the mass versus radius curves show the typical behavior found within the frame of General Relativity. However, we also find a new branch of stellar configurations that can violate the general relativistic causal limit and that in principle may have an arbitrarily large mass. The stars belonging to this new branch are supported against collapse by the nonlocal effects of the bulk on the brane. We also show that these stars are always stable under small radial perturbations. These results support the idea that traces of extra-dimensions might be found in astrophysics, specifically through the analysis of masses and radii of compact objects.
José D.V. Arbañil and M. Malheiro
IOP Publishing
The influence of the anisotropy in the equilibrium and stability of strange stars is investigated through the numerical solution of the hydrostatic equilibrium equation and the radial oscillation equation, both modified from their original version to include this effect. The strange matter inside the quark stars is described by the MIT bag model equation of state. For the anisotropy two different kinds of local anisotropic σ = pt−pr are considered, where pt and pr are respectively the tangential and the radial pressure: one that is null at the star's surface defined by pr(R) = 0, and one that is nonnull at the surface, namely, σs = 0 and σs ≠ 0. In the case σs = 0, the maximum mass value and the zero frequency of oscillation are found at the same central energy density, indicating that the maximum mass marks the onset of the instability. For the case σs ≠ 0, we show that the maximum mass point and the zero frequency of oscillation coincide in the same central energy density value only in a sequence of equilibrium configurations with the same value of σs. Thus, the stability star regions are determined always by the condition dM/dρc > 0 only when the tangential pressure is maintained fixed at the star surface's pt(R). These results are also quite important to analyze the stability of other anisotropic compact objects such as neutron stars, boson stars and gravastars.
P.H.R.S. Moraes, José D.V. Arbañil, and M. Malheiro
IOP Publishing
In this article we study the hydrostatic equilibrium configuration of neutron stars and strange stars, whose fluid pressure is computed from the equations of state p=ωρ5/3 and p=0.28(ρ−4ℬ), respectively, with ω and ℬ being constants and ρ the energy density of the fluid. We start by deriving the hydrostatic equilibrium equation for the f(R,T) theory of gravity, with R and T standing for the Ricci scalar and trace of the energy-momentum tensor, respectively. Such an equation is a generalization of the one obtained from general relativity, and the latter can be retrieved for a certain limit of the theory. For the f(R,T)=R+2λ T functional form, with λ being a constant, we find that some physical properties of the stars, such as pressure, energy density, mass and radius, are affected when λ is changed. We show that for a fixed central star energy density, the mass of neutron and strange stars can increase with λ. Concerning the star radius, it increases for neutron stars and it decreases for strange stars with the increment of λ. Thus, in f(R,T) theory of gravity we can push the maximum mass above the observational limits. This implies that the equation of state cannot be eliminated if the maximum mass within General Relativity lies below the limit given by observed pulsars.
J D V Arbañil and M Malheiro
IOP Publishing
The radial oscillations of charged strange quark stars is investigated. It is considered that the fluid pressure follows the MIT bag model equation of state and the charge density to be proportional to the energy density, ρe = αρ (where α is proportionality constant). The modified equations of radial oscillations to the introduction of the electric charge are integrated to determine the fundamental mode. It is found that the stability of the charged object decreases with the increment of the central energy density and with the growth of the charge fraction.
José D. V. Arbañil and Manuel Malheiro
AIP Publishing LLC
We investigate the hydrostatic equilibrium and the stability of charged stars made of a charged perfect fluid. The matter contained in the star follows the MIT bag model equation of state and the charge distribution to a power-law of the radial coordinate. The hydrostatic equilibrium and the stability of charged strange stars are analyzed using the Tolman-Oppenheimer-Volkoff equation and the Chandrasekhar’s equation pulsation, respectively. These two equation are modified from their original form to the inclusion of the electric charge. We found that the stability of the star decreases with the increment of the central energy density and with the increment of the amount of charge.