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Title Astrophysical consequences of phase transition in millisecond pulsars
Alternative Title Αστροφυσικές συνεπείς της αλλαγής φάσης σε πάλσαρ του χιλιοστού του δευτερολέπτου
Author Ασπραδάκης, Νικόλας
Thesis advisor Αντωνιάδης, Γιάννης
Abstract In a low mass binary system with a neutron star as the primary star and a star in the main sequence phase as its companion, after the end of the accretion process, where we have a MSPs-WD system, the orbit due to tidal forces should be almost circular with eccentricity equal to zero. However the observations of some eccentric binaries have shown that something making the system to have a more elliptical orbit with e ≃ 0.1. The explanation we will try to give here is based on the theory of strange stars and the phase-transition from baryonic matter to quark matter which causes an asymmetric kick that disrupts the system and changes the eccentricity of the orbit. We want to have a better understanding to what is the relationship between the the mass and radius of a neutron star in order to have the phase-transition from the different layers of the pulsar’s core. In order for us to investigate this phenomena, we will use a software program called MESA, that can simulate the stellar evolution of a star, or in our case a binary system of a neutron star and a main sequence star that will eventually evolve in a millisecond pulsar-white dwarf system. This simulation will provide us with information regarding the quantities that we are interested (mass, radius, spin period etc). After collecting the necessary data, we will import them to the evolution code concerning the spin evolution, the mass transfer process and the accretion torque mechanism that we wrote on using python, we proceeded with further analysis for this project. In the first chapter we present a thorough theoretical background about stellar evolution, binary evolution and phase transition from baryonic matter to quark matter. At the end of this chapter there will be a brief talk about the purpose of the thesis. In the second chapter we discuss about the numerical tools and the code about the evolution of the binary we want to study through the simulation that MESA can provide. There will be a discussion about the polytropic equation of state that we choose to use, the evolution of angular momentum, the spin evolution and the parameters we used. We will also analyze the accretion process and torque provided by both Tauris and Bhattacharyya. In the third chapter we will present the results of this analysis and compare the different cases we chose to study. To finish the thesis, in the final chapter we present the conclusions regarding the project and a brief discussion about future projects and changes to make the analysis more clear and correct problematic parts.
Language English
Issue date 2024-03-29
Collection   School/Department--School of Sciences and Engineering--Department of Physics--Graduate theses
  Type of Work--Graduate theses
Permanent Link https://elocus.lib.uoc.gr//dlib/f/e/0/metadata-dlib-1709210382-522850-7293.tkl Bookmark and Share
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