BINARY STARS AND STAR FORMATION

Currently, most stars are thought to be in multiple star systems; at least 50 % of all stars and perhaps 80 % of all stars are in multiple systems. Further, many of the remaining stars may have planetary companions. The relevant question is then,



When do binary star systems form? Is binary formation a part of the star formation process or does binary formation occur after individual stars have formed?




The binary frequency with respect to the orbital period for pre-Main Sequence binaries and Main Sequence binaries.




The binary eccentricity distribution for pre-Main Sequence binaries and Main Sequence binaries




A theoretical Hertzsprung-Russell diagram for pre-Main Sequence stars and observed pre-Main Sequence stars in binary systems.

Apparently, binary star formation takes place very early in the star formation process, well before the individual stars form. The party line is that long period binaries form through fragmentation during dynamical collapse while short period systems form through fission, disk instabilities and interactions, or capture.