Time-dependent, compositionally driven convection in the oceans of accreting neutron stars

Understand

We discuss the effect of chemical separation as matter freezes at the base of the ocean of an accreting neutron star, and the subsequent enrichment of the ocean in light elements and inward transport of heat through convective mixing.

• We extend the steady-state results of Medin & Cumming 2011 to transiently accreting neutron stars, by considering the time-dependent cases of heating during accretion outbursts and cooling during quiescence.
• Convective mixing is extremely efficient, flattening the composition profile in about one convective turnover time (weeks to months at the base of the ocean).
• During accretion outbursts, inward heat transport has only a small effect on the temperature profile in the outer layers until the ocean is strongly enriched in light elements, a process that takes hundreds of years to complete.