Two branches of neutron stars - reconciling a 2M sun pulsar and SN1987A - AstrophysicsReport as inadecuate

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Abstract: The analysis of SN1987A led Brown and Bethe (1995) to conclusion, that themaximum mass of cold neutron stars is low, M max ~ 1.5M sun. Such a low M max,due to a kaon condensation in the stellar core, implies collapse of a toomassive deleptonized protoneutron star into a black hole. This would naturallyexplain the lack of a neutron star in the SN1987A remnant. On the other hand,recent evaluation of mass of PSR J0751+1807 gives M max > 2M sun. Thiscontradicts the original Bethe-Brown model, but can be reconciled withinscenarios proposed in the present Letter. We consider two types of dense mattermodels with high-density softening, due to a transition from a non-strangeN-phase of matter to a strangeness carrying phase S: kaon condensation anddeconfinement of quarks. Two scenarios of neutron star formation in stellarcore collapse are considered. In the first scenario, realized in sufficientlyhot and dense supernova cores, nucleation of an S-phase is sufficiently rapidso as to form an S-phase core, and implying M max = M^S max =~ 1.5M sun. In thesecond scenario, nucleation of the S-phase at neutron star birth is too slow tomaterialize, and the star becomes cold without forming an S-phase core. Then,stellar mass can increase via accretion, until central density ho crit isreached, and the S phase forms. This N branch of neutron stars ends atM=M crit. We select several models of N-phase satifying the necessary conditionM^N max > 2M sun and combine them with models of kaon condensation and quarkdeconfinement. For kaon condensation, we get M crit =~ M^S max =~ 1.5M sun,which is ruled out by PSR J0751+1807. On the contrary, for the EOSs with quarkdeconfinement we get M crit =~ M^N max > 2M sun, which reconciles SN1987A andPSR J0751+1807.

Author: P. Haensel, M. Bejger, J.L. Zdunik


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