DIRECT URCA PROCESSES INVOLVING HYPERONS AND COOLING OF NEUTRON-STARS

We study the effect of the presence of hyperons in dense matter on the neutron star cooling. For several neutron star masses, we consider different scenarios for the stellar interior (with and without nucleon superfluidity), and for the outer layers of the star (with and without strong magnetic field). In the presence of nucleon superfluidity, cooling of a massive neutron star is dominated by the neutrino losses from the direct URCA processes involving hyperons only. Strong surface magnetic field can have a significant effect on the cooling curve. Comparison with recent determination of the effective surface temperature of PSR 0656+14 seems to indicate, that either it does not contain hyperons, or hyperons are superfluid.