Phase Transition Effects on the Dynamical Stability of Hybrid Neutron Stars

• Published in: The Astrophysical journal Vol. 860; no. 1; pp. 12 - 25
• Main Authors: Pereira, Jonas P., Flores, César V., Lugones, Germán
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 10.06.2018; IOP Publishing
• Subjects: Astronomical models; Astrophysics; dense matter; Dynamic stability; gravitation; Mean field theory; Neutron stars; Phase transitions; Quarks; Relativism; Relativistic effects; Relativistic theory; stars: neutron; stars: oscillations (including pulsations); Static stability; Stellar models; Stellar rotation
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/1538-4357/aabfbf

We study radial oscillations of hybrid nonrotating neutron stars composed by a quark matter core and hadronic external layers. At first, we physically deduce the junction conditions that should be imposed between the two phases in these systems when perturbations take place. Then we compute the oscillation spectrum focusing on the effects of slow and rapid phase transitions at the quark-hadron interface. We use a generic MIT-bag model for quark matter and a relativistic mean field theory for hadronic matter. In the case of rapid transitions at the interface, we find a general relativistic version of the reaction mode that has similar properties as its classical counterpart. We also show that the usual static stability condition ∂M/∂ c ≥ 0, where c is the central density of a star whose total mass is M, always remains true for rapid transitions but breaks down in general for slow transitions. In fact, for slow transitions, we find that the frequency of the fundamental mode can be a real number (indicating stability) even for some branches of stellar models that verify ∂M/∂ c ≤ 0. Thus, when secular instabilities are suppressed, as expected below some critical stellar rotation rate, the existance of twin or even triplet stars with the same gravitational mass but different radii, with one of the counterparts having ∂M/∂ c ≤ 0, would be possible. We explore some astrophysical consequences of these results.