Strangeness and Metastable Neutron Stars: What Might have Happened to SN1987A

Immediately after they are born, neutron stars are characterized by an entropy per baryon of order unity and by the presence of trapped neutrinos. If the only hadrons in the star are nucleons, these effects slightly reduce the maximum mass relative to cold, catalyzed matter. However, if stangeness-bearing hyperons, a kaon condensate, or quarks are also present, these effects result in an increase in the maximum mass of up to $\sim 0.3{\rm M}_{\odot}$ compared to that of a col...

A protoneutron star is formed immediately after the gravitational collapse of the core of a massive star. At birth, the hot and high density matter in such a star contains a large number of neutrinos trapped during collapse. Trapped neutrinos generally inhibit the presence of exotic matter -- hyperons, a kaon condensate, or quarks. However, as the neutrinos diffuse out in about 10-15 s, the threshold for the appearance of strangeness is reduced; hence, the composition and the...

We investigate the structure of neutron stars shortly after they are born, when the entropy per baryon is of order 1 or 2 and neutrinos are trapped on dynamical timescales. In all cases, the thermal effects for an entropy per baryon of order 2 or less are small when considering the maximum neutron star mass. Neutrino trapping, however, significantly changes the maximum mass due to the abundance of electrons. When matter is allowed to contain only nucleons and leptons, trappin...

In this contribution the role of strangeness in astrophysics is discussed and, more precisely, strange hadronic matter in the interior of neutron stars. A special attention is payed to certain phenomena involving strange hadronic matter, such as the hyperon puzzle, kaon condensation and the thermal behaviour of hyperons in neutron star mergers.

We present simulations of the evolution of a proto-neutron star in which kaon-condensed matter might exist, including the effects of finite temperature and trapped neutrinos. The phase transition from pure nucleonic matter to the kaon condensate phase is described using Gibbs' rules for phase equilibrium, which permit the existence of a mixed phase. A general property of neutron stars containing kaon condensates, as well as other forms of strangeness, is that the maximum mass...

The standard model for Type II supernovae explosion, confirmed by the detection of the neutrinos emitted during the supernova explosion, predicts the formation of a compact object, usually assumed to be a neutron star. However, the lack of the detection of a neutron star or pulsar formed in the SN 1987A still remains an unsolved mystery. In this paper we suggest that the newly formed neutron star at the center of SN1987A may undergo a phase transition after the neutrino trapp...

The neutrino burst detected during supernova SN1987A is explained in a strangeon star model, in which it is proposed that a pulsar-like compact object is composed of strangeons (strangeon: an abbreviation of "strange nucleon"). A nascent strangeon star's initial internal energy is calculated, with the inclusion of pion excitation (energy around 10^53 erg, comparable to the gravitational binding energy of a collapsed core). A liquid-solid phase transition at temperature ~ 1-2 ...

We discuss different exotic phases and components of matter from the crust to the core of neutron stars based on theoretical models for equations of state relevant to core collapse supernova simulations and neutron star merger. Parameters of the models are constrained from laboratory experiments. It is observed that equations of state involving strangeness degrees of freedom such as hyperons and Bose-Einstein condensates are compatible with 2M$_{solar}$ neutron stars. The rol...

The neutrino signal from SN~1987A provides an excellent opportunity to constrain physical theories for matter at extreme conditions and properties of particles that are produced in supernova (SN) cores. Phase transitions in the supranuclear equation of state (EOS) may change the cooling history of the collapsed stellar core and may even lead to a collapse of the protoneutron star to a black hole on a time scale of several seconds. The implications of such a scenario for the c...

We discuss the role of strangeness on the internal constitution and structural properties of neutron stars. In particular, we report on recent calculations of hyperon star properties derived from microscopic equations of state for hyperonic matter. Next, we discuss the possibility of having a strange quark matter core in a neutron star, or the possible existence of strange quark matter stars, the so-called strange stars.