Nuclear collisions can compress nuclear matter to densities achieved within neutron stars and within core-collapse supernovae. These dense states of matter exist momentarily before expanding. We analyzed the flow of matter to extract pressures in excess of 10 34 pascals, the highest recorded under laboratory-controlled conditions. Using these analyses, we rule out strongly repulsive nuclear equations of state from relativistic mean field theory and weakly repulsive equations of state with phase transitions at densities less than three times that of stable nuclei, but not equations of state softened at higher densities because of a transformation to quark matter.

https://science.sciencemag.org/content/sci/298/5598/1592.full.pdf

Determination of the equation of state of dense matter.

Neutron Stars 1: Equation of State and Structure

Strange quark matter and compact stars

We study the effects of very strong magnetic fields on the equation of state (EOS) in multicomponent, interacting matter by developing a covariant description for the inclusion of the anomalous magnetic moments of nucleons For the description of neutron star matter, we employ a field-theoretical approach, which permits the study of several models that differ in their behavior at high density Effects of Landau quantization in ultrastrong magnetic fields (B > 1014 G) lead to a reduction in the electron chemical potential and a substantial increase in the proton fraction We find the generic result for B > 1018 G that the softening of the EOS caused by Landau quantization is overwhelmed by stiffening due to the incorporation of the anomalous magnetic moments of the nucleons In addition, the neutrons become completely spin polarized The inclusion of ultrastrong magnetic fields leads to a dramatic increase in the proton fraction, with consequences for the direct Urca process and neutron star cooling The magnetization of the matter never appears to become very large, as the value of |H/B| never deviates from unity by more than a few percent Our findings have implications for the structure of neutron stars in the presence of large frozen-in magnetic fields

https://iopscience.iop.org/article/10.1086/309010/pdf

The Equation of State of Neutron Star Matter in Strong Magnetic Fields

With the discovery of massive neutron stars such as PSR J1614-2230, the question has arisen of whether exotic matter such as hyperons can exist in the neutron star core. We examine the conditions under which hyperons can exist in massive neutron stars. We consistently investigate the vector baryon-meson coupling, going from the SU(6) quark model to a broader SU(3) symmetry. We propose that the maximum neutron star mass decreases linearly with the strangeness content ${f}_{s}$ of the neutron star core as ${M}_{\text{max}}({f}_{s})={M}_{\text{max}}(0)\ensuremath{-}0.6{M}_{\ensuremath{\bigodot}}({f}_{s}/0.1)$, which seems to be independent of the underlying nuclear equation of state and the vector baryon-meson coupling scheme. Thus, pulsar mass measurements can be used to constrain the hyperon fraction in neutron stars.

Hyperons and massive neutron stars: Vector repulsion and SU(3) symmetry

Properties of neutron stars derived from the hybrid derivative coupling model of nuclear field theory are studied. Generalized beta equilibrium with all baryon types to convergence is allowed. Hyperon couplings compatible with the inferred binding energy of the lambda hyperon in saturated nuclear matter predict a large hyperon population, with neutrons having a bare majority population in a 1.5{ital M}{sub {circle dot}} neutron star. Among the properties studied are the limits on rotation imposed by gravitation-radiation-reaction instabilities as moderated by viscosity. These instabilities place a lower limit on rotational periods of neutron and hybrid stars of about 1 ms.

S.A. Moszkowski

Papers

Neutron stars in the derivative coupling model.