Common Envelope Evolution

The short period binary system are thought to result from a prior phase of common envelope evolution. Although some observational evidence favors this hypothesis, theoretical calculations have not yet been able to demonstrate convincingly that it is correct. Recently, improvements in the theory have resulted by extension of the numerical simulations to two space dimensions. These calculations now indicate that ejection of much of the common envelope is probable, but that the eventual formation of a short period binary is still uncertain.