Abstract
A neutron star was first detected as a pulsar in 1967. It is one of the most mysterious compact objects in the universe, with a radius of the order of 10 km and masses that can reach two solar masses. In fact, neutron stars are star remnants, a kind of stellar zombie (they die, but do not disappear). In the last decades, astronomical observations yielded various contraints for neutron star masses, and finally, in 2017, a gravitational wave was detected (GW170817). Its source was identified as the merger of two neutron stars coming from NGC 4993, a galaxy 140 million light years away from us. The very same event was detected in γ-ray, X-ray, UV, IR, radio frequency and even in the optical region of the electromagnetic spectrum, starting the new era of multi-messenger astronomy. To understand and describe neutron stars, an appropriate equation of state that satisfies bulk nuclear matter properties is necessary. GW170817 detection contributed with extra constraints to determine it. On the other hand, magnetars are the same sort of compact object, but bearing much stronger magnetic fields that can reach up to 1015 G on the surface as compared with the usual 1012 G present in ordinary pulsars. While the description of ordinary pulsars is not completely established, describing magnetars poses extra challenges. In this paper, I give an overview on the history of neutron stars and on the development of nuclear models and show how the description of the tiny world of the nuclear physics can help the understanding of the cosmos, especially of the neutron stars.
Highlights
Two of the known existing interactions that determine all the conditions of our Universe are of nuclear origin: the strong and the weak nuclear forces
It is not possible to talk about neutron stars without understanding them, and especially the strong nuclear interaction, which is well described by the Quantum Chromodynamics (QCD)
Based on the discovery of asymptotic freedom [1], which predicts that strongly interacting matter undergoes a phase transition from hadrons to the quark–gluon plasma (QGP) and on the possibility that a QGP could be formed in heavy-ion collisions, the QCD phase diagram has been slowly revealed
Summary
Two of the known existing interactions that determine all the conditions of our Universe are of nuclear origin: the strong and the weak nuclear forces. It is not possible to talk about neutron stars without understanding them, and especially the strong nuclear interaction, which is well described by the Quantum Chromodynamics (QCD). While asymptotic freedom is expected to take place at both high temperatures, as in the early universe and high densities, as in neutron star interiors, heavy-ion collisions can be experimentally tested with different energies at still relatively low densities but generally quite high temperatures. I present a comprehensive review of the main nuclear physics properties that should be satisfied by equations of states aimed to describe nuclear matter, the consequences arising from the extrapolation necessary to describe objects with such high densities as neutron stars, and how they can be tuned according to observational constraints. Universe 2021, 7, 267 garded, but the interested reader can certainly use it as an initiation to the physics of these compact objects
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