Hyperon Star Matter

Abstract

HYPERON stars are neutron stars with a superdense core (ρ>1015 g cm−3) consisting chiefly of baryons and heavier resonances. The equation of state for such a multi-component system is determined by the elementary particle spectrum. This spectrum is known to be exponential up to about 2 GeV (ref. 1) For higher energies there is a worsening of experimental knowledge. We assume the exponential behaviour to continue (ref. 1 and unpublished work of Krzywicki) beyond 2 GeV, and take into account the fermions only, which yields in the low temperature limit the Hansen results2. Then the equation of state becomes temperature dependent because the heaviest components are partially nondegenerate. If the core of the hyperon star is in general relativistic thermal equilibrium, the poly tropic index of the relation between pressure and total density (including kinetic energy) proves to be negative. As a consequence the velocity of sound in the radial direction, defined by decreases towards the centre instead of exceeding the velocity of light3. Under the additional hypothetical supposition that the mass spectrum remains exponential up to infinity (infinite energies), in hyperon stars the temperature cannot exceed a limiting temperature of T0 = 2 × 1012 K and the time component g00 of the metric tensor of space-time cannot become zero.