Thesis


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Academic Year
2011 / 2012
Title
The physics of compact stars
Domain
Astrophysics
Abstract
The physics of Compact stars Nuclear astrophysics is a blooming area where compact stars play an essential role and which requires the contribution of different areas of physics, namely, nuclear and particle physics, astrophysics, gravitational and computational physics. The present proposal aims at investigating several aspects of compact stars:
a) The very recent measurement (Demorest et al. 2010) of the Shapiro delay in the binary millisecond pulsar J1614-2230 has permitted to obtain the mass of the associated neutron star. The calculated mass is M = (1.97 $\pm$ 0.04)M (Demorest et al. 2010), making PSR J1614-2230 the most massive neutron star known to date. As it is well known that neutron star mass measurements give one of the most stringent tests on the composition and EOS of strong interacting matter at very high densities. The possibility that this star contains a quark core, and therefore is an hybrid star, or is a quark star will be investigated within a recently proposed nonlocal Nambu--Jona-Lasinio type model. In this model the two point function is parameterized by a functional form which is compatible with the Dyson-Schwinger and lattice QCD results Pedro Costa, O. Oliveira, P. J. Silva, (Phys.Lett.B695:454-458,2011)
b) The effects of quark matter nucleation on the evolution of proto–neutron stars is dependent on the surface energy of a quark droplet in a hadronic matter backgrount. There is a large uncertainty about this quantity. Using several quark models which reproduce low energy meson properties this quantity will be calculated. The implications on the quark nucleation process discussed in (Ignazio Bombaci, Irene Parenti, Isaac Vidaña, Astrophys.J. 614 (2004) 314-325 and I. Bombaci, D. Logoteta, P.K. Panda, C. Providencia, I. Vidana, Physics Letters B 680 (2009) 448-452) will be discussed.
c) The pressure at the core-crust transition is important to determine the mass of the crust, which is one of the basic quantities needed to interprete observational data related to starquakes, glitches and X-ray transcients. Using the correlations between astrophysical properties and nuclear observables steblished in recent works, extract the 0 consequences for the mass and width of the crust, by getting the star profile solving the Tolman–Oppenheimer–Volkoff (TOV) equation. This problem also depends on the inner region of the star, which is not well-known. We will compare the uncertainties arising from the equation of state of very dense matter to those related to the EOS at saturation and sub-saturation density. Within the relativistic effective models, we will perform a self-consistent calculation of the mass-radius relation for the whole star starting from the center.
d) The neutrino mean-free path is reduced in a clusterized medium, and this is expected to play a role in the shock revival needed in the simulations of supernova explosions. The effect of neutrino trapping in beta-equilibrium matter on the pasta phase will be studied within relativistic mean-field theory and density dependent relativistic models. Neutrino properties, which are needed to estimate the neutrino-trapping rate which is an input for the study. depend on the structure and composition of the clusterized system. We will compare in a systematic way the typical cluster size, geometry and composition obtained in equilibrium calculations of non-homogeneous matter with those induced by finite-size instabilities at zero and finite temperature. The possible dependence of the results on the density dependence of the symmetry energy should be investigated. The neutrino mean free path inside dense and hot hadronic matter is a very important quantity in the studies of core collapse supernovae, and formation and evolution of neutron stars. This quantity must be calculated in warm stellar matter with trapped neutrinos in the pasta phase.
Institution
grants the Degree
U. Coimbra
Host Institution
Centro de Física Computacional
Supervisor
Constança Providência
Co-Supervisor