The collapse of carbon-oxygen white dwarfs

Abstract

Carbon-oxygen white dwarfs formed in close binary systems may become unstable by mass accretion. Recent results concerning carbon-oxygen separation at the freezing point during the phase of cooling may have very important consequences for the problem of neutron star formation. The central, high-density regions of the star are then made of pure oxygen, the carbon being rejected to lower-density layers. When the star is compressed, carbon ignition can only happen after neutronization of the central (oxygen) regions. It is shown that, in this case, the chances of collapse to a neutron star are independent from the rate of mass accretion, in contrast with previous studies. A likely mechanism for neutron star formation emerges from this picture.