Thermodynamic instabilities in warm and dense asymmetric nuclear matter and in compact stars

A Lavagno,G Gervino,D Pigato

doi:10.1088/1742-6596/665/1/012072

Abstract

We investigate the possible thermodynamic instability in a warm and dense nuclear medium where a phase transition from nucleonic matter to resonance-dominated Δ-matter can take place. Such a phase transition is characterized by both mechanical instability (fluctuations on the baryon density) and by chemical-diffusive instability (fluctuations on the isospin concentration) in asymmetric nuclear matter. Similarly to the liquid-gas phase transition, the nucleonic and the Δ-matter phase have a different isospin density in the mixed phase. In the liquid-gas phase transition, the process of producing a larger neutron excess in the gas phase is referred to as isospin fractionation. A similar effects can occur in the nucleon- Δmatter phase transition due essentially to a Δ- excess in the Δ-matter phase in asymmetric nuclear matter. In this context we also discuss the relevance of Δ-isobar degrees of freedom in the bulk properties and in the maximum mass of compact stars.

Highlights

One of the very interesting aspects in nuclear astrophysics and in the heavy-ion collisions experiments is a detailed study of the thermodynamical properties of strongly interacting nuclear matter away from the nuclear ground state.The new accumulating data from x-ray satellites provide important information on the structure and formation of compact stellar objects
The information coming from experiments with heavy ions in intermediateand high-energy collisions is that the equation of state (EOS) depends on the energy beam and sensibly on the electric charge fraction Z/A of the colliding nuclei, especially at not too high temperature [1, 2, 3, 4]
The study of nuclear matter with arbitrary electric charge fraction results to be important in radioactive beam experiments and in the physics of compact stars