Hadronic phase transitions at supranuclear densities and the delayed collapse of newly formed neutron stars.

Details Hadronic phase transitions at supranuclear densities and the delayed collapse of newly formed neutron stars. Hadronic phase transitions at supranuclear densities and the delayed collapse of newly formed neutron stars.

Apr 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...296..145k&link_type=abstract

Astronomy and Astrophysics, v.296, p.145

Astronomy and Astrophysics

Astrophysics

115

Stars: Neutron, Supernovae: General, Supernovae: Individual: Sn 1987A, Dense Matter, Equation Of State, Elementary Particles

Scientific paper

We present numerical simulations of the neutrino-driven deleptonization and cooling of newly formed, hot, lepton-rich neutron stars. In particular, we are interested in the effects associated with the creation of additional hadronic states like hyperons and {DELTA}-resonances at densities of a few times nuclear density. Due to the occurrence of these baryonic components besides neutrons and protons, the considered objects are nuclear matter stars rather than neutron stars. The hyperonic equation of state employed in this work yields stable, lepton-rich stars with a maximum (baryonic) mass which is higher by about {DELTA}M_b_~0.17Msun_ compared with the stability limit of M_b_^max^~1.77Msun_ for deleptonized, cold matter. We find stars in the range 1.77Msun_<~M_b_<~1.94Msun_ to be stabilized for an intermediate phase following their formation in the gravitational collapse of the stellar core. They become unstable against gravity after they have lost a significant fraction of their leptons, but long before they have cooled down. Typically, this stable period lasts for a few seconds up to about ten seconds. We do not see much of a stabilizing influence of thermal pressure, but thermal energy contributes to the gravitating mass and may bring the star higher above the stability limit in the deleptonized state, M_g_^max^=~1.58Msun_. Thus the additional mass that is supported by thermal pressure of baryons turns out to be quite small, and the window of stabilized masses is increased by less than 0.1Msun_ to be about {DELTA}M_b_=~0.25Msun_ for hot stars. We calculate the expected neutrino signals in the Kamiokande II and IMB detectors for our sample of protoneutron star models and compare with characteristic parameters of the neutrino observation in connection with SN 1987A. Since our unstable stars approach the moment of dynamical collapse while they gradually become more and more compact, their continuously increasing gravitational redshift and rising neutrino opacity suppress the observable neutrino signal, until the neutrino emission is finally chopped off at the onset of collapse. We do not find an indication of a late outburst of neutrino radiation.

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