THE EFFECT OF DIRECT URCA PROCESSES ON THE OHMIC DECAY OF THE MAGNETIC-FIELD

Recent work has shown that direct Urca processes can occur in the inte riors of neutron stars that are sufficiently massive. Direct Urca proc esses considerably speed up the cooling of neutron stars, thereby acce lerating the decay of the magnetic field in their cores. We included t he latter effect in calculations of the evolution of magnetic fields o f neutron stars. It is shown that the decay timescale reduces consider ably and becomes on the order of 10(4) to 10(5) years. Thus, all neutr on stars can be separated into two populations. The more massive ones cool quickly and their magnetic fields decay rapidly, whereas these pr ocesses proceed more slowly in the less massive stars.