Double core evolution. I. A 16 M sun star with a 1 M sun neutron-star companion.

The penetration of an orbiting 1 solar mass neutron star into a 16 solar mass supergiant companion is investigated. Primary emphasis is placed on the structure and evolution of the massive component. Effects due to turbulent dissipation and frictional drag as well as angular momentum transport are included. It is found that double core evolution leads to either (1) hydrodynamic ejection of part or all of the envelope or (2) coalescence of the two cores with little or no mass ejection - possibly resulting in a Thorne-Zytkow object. Some implications regarding the binary pulsar are discussed in the context of the double core scenario.