Regions of violent star formation such as supergiant HII regions or superassociations often reveal a binary space structure: they contain two separate components within which very intensive star formation proceeds more or less simultaneously. This observational fact suggests an evolutionary scenario for the phenomenon, in which the key role is played by a strong collision of shock fronts produced by the energy release of the previous generation of massive stars in the region.

Binary stuctures and nonlinear gas dynamics

There are well observed giant regions of intensive star formation – superassociations – that consist of two (or three) components: Per-Cas, Sco-Cen and Car in the Milky Way, OB 78 in M31, Region IV = 30 Dor E + 30 Dor W in the LMC (Efremov 1988, 1989). A dust lane is observed in some cases between the two parts of the region that makes this composite structure especially obvious. In regions like OB 21 in M31, HII clouds give an even more contrasting picture when they concentrate at the two opposite sides of the dust lane.

Can this binary spatial structure be a clue to the physical nature of the violent star formation phenomenon? We assume that the answer to this question is positive and present it here in the form of an evolutionary scenario in which shock-shock collisions in the interstellar gas play a key role.