No abstract

A static and spherically symmetric stellar model is described by a perfect charged fluid. Its construction is done using the solution of the Einstein–Maxwell equations for which we specify the temporal metric and the electric field which is a monotonic increasing function null in the center. The density, pressure and speed of sound turn out to be regular functions, positive and monotonic decreasing as function of the radial distance. Also, the speed of sound is lower than the speed of light, that is to say, it does not violate the condition of causality. The value of compactness [Formula: see text], so the model is useful to represent neutron stars of quark stars. In a complementary manner, we report the physical values when describing a star of mass [Formula: see text] and radius [Formula: see text], in such case [Formula: see text], and given the presence of the charge, the interval for the central density [Formula: see text].

Starting from the construction of a solution for Einstein’s equations with a perfect fluid for a static spherically symmetric spacetime, we present a model for stars with a compactness rate of [Formula: see text]. The model is physically acceptable, that is to say, its geometry is non-singular and does not have an event horizon, pressure and speed of sound are bounded functions, positive and monotonically decreasing as function of the radial coordinate, also the speed of sound is lower than the speed of light. While it is shown that the adiabatic index [Formula: see text], which guarantees the stability of the solution. In a complementary manner, numerical data are presented considering the star PSR J0737-3039A with observational mass of [Formula: see text], for the value of compactness [Formula: see text], which implies the radius [Formula: see text] and the range of the density [Formula: see text] [Formula: see text], where [Formula: see text] and [Formula: see text] are the central density and the surface density, respectively. This range is consistent with the expected values; as such, the model presented allows to describe this type of stars.

A stellar model with anisotropic pressure is constructed and analyzed, the metric components that describe the geometry and the source of matter satisfy Einstein’s equations and both are finite inside the star. In addition, density and pressure are decreasing monotone functions of the radial distance. The speed of sound is positive and less than the speed of light, furthermore the model is potentially stable. The model allows describing compact objects with compactness of [Formula: see text] and as a result of the anisotropic value there is a range of values of the central density, in particular for the maximum value of compactness a star with [Formula: see text] and a value of anisotropic parameter [Formula: see text] we get a stellar radius of [Formula: see text] and a central density [Formula: see text]. The above makes the solution a physically realistic model that can be used to describe dense objects such as neutron stars whose characteristic density is of the order of nuclear density.

Starting from a perfect fluid solution we constructed a generalization with anisotropic pressures and regular geometry as well as the pressures, the density and the speed of sound, these are also positive and monotonic decreasing functions. The speed of sound is lower than the speed of light, that is to say, the condition of causality is not broken. The model satisfies all the energy conditions and the radial [Formula: see text] and tangential [Formula: see text] speeds and complies with [Formula: see text] because of this the solution is stable according to the stability criteria related with the concept of cracking. The maximum value of the compactness factor [Formula: see text] which is lower than the Buchdahl limit and associated to neutron stars. In a complementary manner, we realize an analysis of the behavior of a star with a mass of [Formula: see text], with a fixed value of the anisotropy parameter and different compactness values, giving as a result that their central density [Formula: see text] and the superficial density [Formula: see text], the maximum values match the value of greater compactness of the model with a stellar radius of 6506.921 m.