Neutron Stars: Celestial Laboratories for Dense Matter

Shriya, Soma (2019) Neutron Stars: Celestial Laboratories for Dense Matter. Masters thesis, Indian Institute of Science Education and Research Kolkata.

PDF (MS dissertation of Soma Shriya (14MS148)) 14MS148.pdf - Submitted Version Restricted to Repository staff only Download (9MB)

Abstract

Supernova explosions are dazzling celestial events that mark the death of massive stars. However, the physics involved in the final stages of the life of a massive star is still not completely understood. Once the fusion reactions in the star come to a halt, the expected consequence is a core collapse supernova and the remnant could either be a neutron star or a black hole. Neutron stars nurture the most densest form of matter in this observable universe. These compact astrophysical objects encompass a wide range of densities from its crust to the core. The knowledge of compositions and equation of state (EoS) of matter in neutron star interior is important to estimate gross properties of neutron stars. Observed mass, radius and moment of inertia are direct probes of compositions and EoS of neutron star matter. In this thesis, we construct equations of state (EoSs) of neutron star matter within the framework of relativistic mean field (RMF) models. Next we calculate mass-radius relationships of non-rotating neutron stars and confront those results with observations. We continue our study on the structures of slowly rotating neutron stars in the Hartle-Thorne formalism. Since it has been postulated that quark matter could be the ground state of dense matter, we also construct EoSs from the MIT Bag Model to calculate structures of quark stars. We repeat the same calculations for quark stars as well. We further find universality relations in certain properties of compact stars. We study these universal relations and understand their significance. Finally we discuss the recent binary neutron star merger GW170817 and its implications to neutron star EoS. The electromagnetic observations that accompanied this merger event along with the study of universal relations enable us to set an upper limit on the maximum mass of a non-rotating neutron star, i.e; ≤ 2:18M⊙. This upper limit on the non-rotating neutron star mass rules out the possibility of the very stiff equations of state which lead to higher maximum masses. Further, the 50%-90% confidence level parameter estimation of tidal deformability of the binary system from the analysis of GW170817 signal yields a constraint on the equations of state. This helps us rule out the very stif equations of state that we have studied. The softer equations of state are however valid according to these bounds. Finally, we extract information about neutron star radii using the upper bound on the combined tidal deformability.

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