Structure and astrophysical properties of dark energy admixed neutron stars

Abstract

The presence of a dark energy (DE) core, made of a Chaplygin dark fluid, is capable of influencing the diverse observable properties of neutron stars (NSs). However, there is also the possibility that NSs could contain a mixture of ordinary nuclear matter and DE. In this perspective, we propose an equation of state (EoS) that includes both normal matter and DE, where a free parameter $f$ quantifies the ratio of DE density with respect to the total energy density. As expected, in the limit $f\to 0$ we recover the already known results corresponding to pure nuclear matter. Remarkably, increasing this fraction $f$ leads to a softer EoS and thus strongly favors the fulfillment of the causality condition. As a consequence of our mass--radius results, the central compact object in HESS J1731-347 can be satisfactorily described as a DE admixed NS. For sufficiently high stellar masses, our calculations further indicate that both the gravitational redshift and the fundamental nonradial oscillation frequency increase significantly with an increasing DE fraction, whereas the opposite trend is observed for the total gravitational mass and tidal deformability. As is typical for compact stars composed purely of ordinary matter, we find that in our DE admixed stellar models the central density corresponding to the maximum-mass configuration coincides with the point at which the squared radial vibration frequency vanishes. Moreover, higher DE concentrations lead to enhanced stability of these configurations.

Comments: 13 pages, 6 figures