Defense
Student: Loreany Ferreira de Araújo
Program: Astronomy
Title: “Possible impacts of the cosmological dark sector on neutron stars"
Advosor: Prof. Dr. José Ademir Sales de Lima - IAG/USP
Judging Comitee:
- Prof. Dr. José Ademir Sales de Lima - Orientador e Presidente - IAG/USP
- Profa. Dra. Elisabeth Maria de Gouveia Dal Pino - IAG/USP (por videoconferência)
- Prof. Dr. Vilson Tonin Zanchin - UFABC
- Dr. José Carlos Neves de Araújo – INPE
- Prof. Dr. Rodolfo Valentim da Costa Lima – UNIFESP (por videoconferência)
- Prof. Dr. Valdir Barbosa Bezerra – UFPB (por videoconferência)
Abstract:
Neutron stars, known for their extremely high densities, are environments
conducive to gravitational interactions. Acknowledging that dark energy and dark
matter account for the largest fractions in the composition of the universe, we
explore a scenario in which these components act jointly with the ordinary matter
of these compact objects. Initially, we assumed a neutron star composed of
baryonic matter and dark energy, the latter characterized as vacuum, with negative
pressure and energy density related by p = ωϵ, with ω = -1. Subsequently, we
consider different values for ω in order to account for the indeterminacy of dark
energy. To incorporate dark matter, we assume that particles are described as a
degenerate Fermi gas and investigate the coupling and interactions between the
fluids. By defining a total energy-momentum tensor, represented by the sum of
each component (baryonic and dark), we examine how the ordinary mass-radius
relations are modified. The main aspect observed with the presence of dark energy
is the reduction in both mass and radius as its percentage increases in the structure
of the star. When varying ω, an approximation to the ordinary case is observed for
values greater than -1, specifically for ω = -0.35. The opposite behavior is observed
for more negative values of ω. Including dark matter mitigates the reductions in
mass and radius, especially in the interacting cases. In such cases, the
independence of the coupling factors α and the interaction Q emerges when the
interaction occurs among the three independent fluids. In the case of a coupled
dark sector, the degeneracy is broken, particularly when larger fractions of dark
energy are adopted. Taking into account neutron star observables, we compare the
effects on tidal deformabilities with the observation of GW170817. Furthermore, we
adopt mass and radius estimates of these objects to constrain the parameters of
the proposed models.
Keywords: neutron stars, dark energy, dark matter, mass-radius relations, tidal deformability