The Evolution of Binaries in a Gaseous Medium: Three-Dimensional Simulations of Binary Bondi-Hoyle-Lyttleton Accretion
Common Envelope Evolution
Common envelope (CE) is an essential phase in the formation of many types of close binary systems. A CE phase occurs when one star in the binary becomes embedded in the expanding envelope of its giant companion. The relative motion between the embedded star and the envelope gas results in drag forces, which deposit orbital kinetic energy into the envelope material. As drag forces strip energy and angular momentum from the orbit, the embedded star spirals deeper within the envelope of the giant. Whether or not the envelope can be completely unbound and the binary survives the encounter depends on the amount of energy the drag forces deposit into the envelope and over what timescale this energy transfer occurs. Our results suggest that the inclusion of realistic density gradients in the calculation of drag forces could result in a shorter CE interaction and a more rapid inspiral than analytical estimates suggest.