A model for low mass compact objects

Abstract

A model for low mass compact objects with compactness ratio $u\leq 0.06092997016$ is presented here. Density, pressure and sound speed are regular and monotonic decreasing functions. The change between the central density $\rho_c$ and the density on the surface $\rho_b$ is lower than $3.94\%$ and the maximum change occurs for the biggest compactness, i.e. $\rho_c=1.039350237\rho_b$. This allows us to apply this model for the case of compact stars in which the density variation is very small. In particular, we can use this model for PSR B0943 + 10, a quark star candidate, with radius $R=2.6{\rm Km}$ and mass $M=0.2 M_\odot$. According to our model it comes out that the density on the surface is $\rho_b=5.388074 \times 10^{17} Kg/m^3$ and its central density $\rho_c=1.007150 \rho_b$ is slightly bigger than the surface density and larger than the nuclear density.

A charged perfect fluid model with high compactness

“…Nowadays it is known that this form guarantees the regularity of the geometry in the vicinity of the center, since for this it is only required that [30] So other functions can be proposed with these properties. The proposed form for the function y(r) and other similar functions have allowed to show the relevance of the existence of anisotropic pressures to be able to have physically acceptable models [31] besides that they have been applied for the description of physically acceptable stellar models [30,32,33], some of which are characterized because the speed of sound is a decreasing monotonic function as a function of the radial coordinate [34]. The construction of interior solutions is useful to have a better clarity of the inner behavior of the stars [12], some solutions with perfect fluid sources without charge [29,35,36] these became generalized to charged case [37][38][39] to represent compact stars.…”

“…The proposal of this section is to obtain a charged model that generalizes to the previously constructed case [22]. Some of the advantages presented by charged models is that their compactness ratio becomes greater than their counterpart without charge as a result of the non-neutrality of the fluid.…”

“…ν ≥ 0 represents the charge parameter that in the case ν = 0 will allow us to recover the solution without electric charge [22]. The shape of the electric field magnitude is not unique, there are a variety of possible acceptable functions for the same function y(r) [37][38][39], the choice of this serves particular interests of the approach of the model to be proposed or of the research proposed, even this can be given through the charge density [40] or through a relationship with the state equation [41].…”

“…The construction of a static and symmetrically spherical space-time is proposed from the assumption of a specific form of gravitational potential g tt [22] and the magnitude of the electric field. The solution satisfies conditions that make it physically acceptable and allows this to represent astrophysical compact stars with a compactness u ≤ 0.5337972212.…”

An interior solution with perfect fluid

“…On the other hand, the stability of the solutions is guaranteed due to the fact that their adiabatic index is a monotonic increasing function with a minimum value γ ≥ 14.615. This exact internal solution can be generalized to the charged or anisotropic case that is able to represent stars with similar characteristics to the ones presented here, with the advantage that the interval of the compactness rate will be greater than in the case of the perfect fluid,[35][36][37] like other solutions with perfect fluid have been generalized [38][39][40][41][42]. Another relevant point is that the solution may be used as2050141-13 Mod.…”