Fragmentation of Neutron Star Matter

P ALCAIN; DORSO, C.O.

New London - New Hampshire

Congreso; Gordon Research Conference - Nuclear Chemistry; 2017

Gordon REsearch Conferences

(Dated: June 1, 2017)Background: Neutron stars are astronomical systems with nucleons submitted to extreme conditions. Due to thelonger range coulomb repulsion between protons, the system has structural inhomogeneities. Several interactionstailored to reproduce nuclear matter plus screened Coulomb term reproduce these inhomogeneities known asnuclear pasta. These structural inhomogeneities, located in the crust of neutron stars, can also arise in expandingsystems depending on the thermodynamic conditions (temperature, proton fraction, . . . ) and the expansionvelocity.Purpose: We aim to find the dynamics of the fragments formation for expanding systems simulated accordingto the little big bang model. This expansion resembles the evolution of neutron stars merger.Method: We study the dynamics of the nucleons with semiclassical molecular dynamics models. Starting with anequilibrium configuration, we expand the system homogeneously until we arrive to an asymptotic configuration (i.e. very low final densities). We study, with four different cluster recognition algorithms, the fragment distributionthroughout this expansion and the dynamics of the cluster formation.Results: Studying the topology of the equilibrium states, before the expansion, we reproduced the known pastaphases plus a novel phase we called pregnocchi, consisting of proton aggregates embedded in a neutron sea. Wehave identified different fragmentation regimes, depending on the initial temperature and fragment velocity. Inparticular, for the already mentioned pregnocchi, a neutron cloud surrounds the clusters during the early stages ofthe expansion, resulting in systems that give rise to configurations compatibles with the emergence of r-proccess.Conclusions: These calculations pave the way to a comparision between Earth experiments and neutron starstudies.