Phase Transitions In Nuclear Matter And Consequences For Neutron Stars

Author : Jacob Brian Roark
Publisher :
ISBN 13 :
Total Pages : 106 pages
Book Rating : 4.:/5 (11 download)

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Download or read book The Deconfinement Phase Transition in Neutron Stars and Proto-neutron Stars written by Jacob Brian Roark and published by . This book was released on 2018 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: Neutron stars have masses between 1 and 2 times the mass of the Sun, all packed into a sphere just 20 to 30 km across (roughly the size of Cleveland). Consequently, neutron stars exhibit some the of highest material densities in the universe, with average densities a little over three times the density of a typical atomic nucleus. Under such astronomical pressures, hadrons can be ``squeezed" until they break apart into their constituent quarks. This phenomenon is known as the deconfinement phase transition and has long been suspected to occur near the core of neutron stars (so-called ``hybrid stars"), perhaps even going as far as producing stars consisting entirely of quark matter (so-called ``quark stars"). Thanks to the macroscopic consequences of this microscopic phase transition, there exists a dynamic interplay between the observations of astronomers and the theoretical models of astrophysicists, making neutron stars opportune natural laboratories for studying nuclear physics.Neutron-star matter resides in the low temperature and high density regime of the phase diagram of quantum chromodynamics (QCD). Because of this, common methods in QCD that describe high-energy matter cannot be directly applied to neutron star matter. For instance, perturbative QCD (PQCD) is limited to systems involving relatively weak interactions. But near the deconfinement phase transition, the coupling strength of the strong interaction becomes large, thus limiting the application of perturbative techniques. Similarly, lattice QCD (LQCD) exhibits the sign problem (where the integral of a highly oscillatory function cannot be numerically solved) in the regime of nonzero baryon density. Therefore, the high density of neutron-star matter means that the application of LQCD is also limited when studying quark deconfinement in the context of neutron stars.In this work, these limitations will lead towards the use of the Chiral Mean Field (CMF) model, an effective relativistic model based on the nonlinear realization of the sigma model. It includes self-consistent chiral symmetry restoration and deconfinement to quark matter. The strong interaction, in reality, is mediated by gluons. But in the context of the CMF model, instead, the effect of gluon exchange is replicated via the exchange of mesons between baryons and quarks, resulting in some of the properties of the quarks and gluons being transferred to these mesons.The case of proto-neutron stars (i.e., very young neutron stars) will also be studied. While neutron stars harbor interior temperatures around 1 MeV, the interior of a proto-neutron star can reach temperatures of around 10 -- 30 MeV, resulting in a dramatic drop in the mean free path of neutrinos. For this reason, in the case of proto-neutron stars, neutrino trapping must be taken into account and lepton fraction must be conserved. It is also necessary to ensure electric charge neutrality for both neutron and proto-neutron stars as a requirement for structural stability, along with other requirements like chemical equilibrium. Given the temperature regimes described above, zero temperature \textit{and} finite temperature calculations will be explored. In addition, the possibility of quark phase and hadronic phase mixtures will be considered in each case. Upon compiling this data and achieving several equations of state for neutron-star and proto-neutron-star matter, the Tolman-Oppenheimer-Volkoff (TOV) equations (derived from general relativity) will be applied, yielding information regarding the large-scale structure of these compact objects.