The fate of a neutron star just below the minimum mass: does it explode?
Abstract
First results of numerical simulations are presented which compute the dynamical evolution of a neutron star with a mass slightly below the minimum stable mass by means of a new implicit (general relativistic) hydrodynamic code. We show that such a star first undergoes a phase of quasistatic expansion, caused by slow nuclear beta decays, lasting for about 20 seconds, but then explodes violently. The kinetic energy of the explosion is around 10(49) erg, the peak luminosity in electron antineutrinos is of order 10(52) erg/s, and the thermodynamic conditions of the expanding matter are favorable for rprocess nucleosynthesis. These results are obtained for the HarrisonWheeler equation of state and a simple and, possibly, unrealistic treatment of beta decay rates and nuclear fission, which were adopted for comparison with previous works. However, we do not expect that the outcome will change qualitatively if more recent nuclear input physics is used. Although our study does not rely on a specific scenario of how a neutron star starting from a bigger (and stable) mass can reach the dynamical phase, we implicitly assume that the final massloss event happens on a very short time scale, i.e., on a time scale shorter than a soundcrossing time, by removing a certain amount of mass as an initial perturbation. This assumption implies that the star has no time to adjust its nuclear composition to the new mass through a sequence of quasiequilibria. In the latter case, however, there exists no stable configuration below the minimum mass, because the equation of state of fully catalyzed matter is too soft. Therefore, the dynamics of the explosion will not be too different from what we have obtained if different initial perturbations are assumed.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 June 1998
 arXiv:
 arXiv:astroph/9707230
 Bibcode:
 1998A&A...334..159S
 Keywords:

 STARS: NEUTRON;
 EQUATION OF STATE;
 HYDRODYNAMICS;
 INSTABILITIES;
 NUCLEAR REACTIONS;
 NUCLEOSYNTHESIS;
 ABUNDANCES;
 Astrophysics
 EPrint:
 10 pages, Latex