Neutron drip transition in accreting and nonaccreting neutron star crusts

Understand

The neutron-drip transition in the dense matter constituting the interior of neutron stars generally refers to the appearance of unbound neutrons as the matter density reaches some threshold density $\rho_\textrm{drip}$.

• This transition has been mainly studied under the cold catalyzed matter hypothesis.
• However, this assumption is unrealistic for accreting neutron stars.
• After examining the physical processes that are thought to be allowed in both accreting and nonaccreting neutron stars, suitable conditions for the onset of neutron drip are derived and general analytical expressions for the neutron drip density and pressure are obtained.