arXiv subjects

R. M. Marinho Jr

Publications and source records attributed to R. M. Marinho Jr.

5 recordsLinked to original sources

arXiv2018

White dwarfs with a surface electrical charge distribution: Equilibrium and stability

The equilibrium configuration and the radial stability of white dwarfs composed of charged perfect fluid are investigated. These cases are analyzed through the results obtained from the solution of the hydrostatic equilibrium equation. We regard that the fluid pressure and the fluid energy density follow the relation of a fully degenerate electron gas. For the electric charge distribution in the object, we consider that it is centralized only close to the white dwarfs' surfaces. We obtain larger and more massive white dwarfs when the total electric charge is increased. To appreciate the effects of the electric charge in the structure of the star, we found that it must be in the order of $10^{20}\,[{\rm C}]$ with which the electric field is about $10^{16}\,[{\rm V/cm}]$. For white dwarfs with electric fields close to the Schwinger limit, we obtain masses around $2\,M_{\odot}$. We also found that in a system constituted by charged static equilibrium configurations, the maximum mass point found on it marks the onset of the instability. This indicates that the necessary and sufficient conditions to recognize regions constituted by stable and unstable equilibrium configurations against small radial perturbations are respectively $dM/dρ_c>0$ and $dM/dρ_c<0$.

astro-ph.SR↗

arXiv2018

General Relativistic effects in the structure of massive white dwarfs

In this work we investigate the structure of white dwarfs using the Tolman-Oppenheimer-Volkoff equations and compare our results with those obtained from Newtonian equations of gravitation in order to put in evidence the importance of General Relativity (GR) for the structure of such stars. We consider in this work for the matter inside white dwarfs two equations of state, frequently found in the literature, namely, the Chandrasekhar and Salpeter equations of state. We find that using Newtonian equilibrium equations, the radii of massive white dwarfs ($M>1.3M_{\odot}$) are overestimated in comparison with GR outcomes. For a mass of $1.415M_{\odot}$ the white dwarf radius predicted by GR is about 33\% smaller than the Newtonian one. Hence, in this case, for the surface gravity the difference between the general relativistic and Newtonian outcomes is about 65\%. We depict the general relativistic mass-radius diagrams as $M/M_{\odot}=R/(a+bR+cR^2+dR^3+kR^4)$, where $a$, $b$, $c$ and $d$ are parameters obtained from a fitting procedure of the numerical results and $k=(2.08\times 10^{-6}R_{\odot})^{-1}$, being $R_{\odot}$ the radius of the Sun in km. Lastly, we point out that GR plays an important role to determine any physical quantity that depends, simultaneously, on the mass and radius of massive white dwarfs.

gr-qc↗

arXiv2017

Stellar equilibrium configurations of white dwarfs in the $f(R,T)$ gravity

In this work we investigate the equilibrium configurations of white dwarfs in a modified gravity theory, na\-mely, $f(R,T)$ gravity, for which $R$ and $T$ stand for the Ricci scalar and trace of the energy-momentum tensor, respectively. Considering the functional form $f(R,T)=R+2λT$, with $λ$ being a constant, we obtain the hydrostatic equilibrium equation for the theory. Some physical properties of white dwarfs, such as: mass, radius, pressure and energy density, as well as their dependence on the parameter $λ$ are derived. More massive and larger white dwarfs are found for negative values of $λ$ when it decreases. The equilibrium configurations predict a maximum mass limit for white dwarfs slightly above the Chandrasekhar limit, with larger radii and lower central densities when compared to standard gravity outcomes. The most important effect of $f(R,T)$ theory for massive white dwarfs is the increase of the radius in comparison with GR and also $f(R)$ results. By comparing our results with some observational data of massive white dwarfs we also find a lower limit for $λ$, namely, $λ>- 3\times 10^{-4}$.

gr-qc↗

arXiv2012

Data Analysis of Gravitational Waves Signals from Millisecond Pulsars

The present work is devoted to the detection of monochromatic gravitational wave signals emitted by pulsars using ALLEGRO's data detector. We will present the region (in frequency) of millisecond pulsars of the globular cluster 47 Tucanae (NGC 104) in the band of detector. With this result it was possible to analyse the data in the frequency ranges of the pulsars J1748-2446L and J1342+2822c, searching for annual Doppler variations using power spectrum estimates for the year 1999. We tested this method injecting a simulated signal in real data and we were able to detect it.

gr-qc↗

arXiv2010

Compact stars with a quark core within NJL model

An ultraviolet cutoff dependent on the chemical potential as proposed by Casalbuoni {\it et al} is used in the su(3) Nambu-Jona-Lasinio model. The model is applied to the description of stellar quark matter and compact stars. It is shown that with a new cutoff parametrization it is possible to obtain stable hybrid stars with a quark core. A larger cutoff at finite densities leads to a partial chiral symmetry restoration of quark $s$ at lower densities. A direct consequence is the onset of the $s$ quark in stellar matter at lower densities and a softening of the equation of state.

nucl-th↗