Colliding interstellar bubbles

Using radio and mm surveys, we have found 20 bubbles that show the presence of both atomic and molecular gas and determined their distances, ages, masses, and energies. In our initial study, we identified two pairs of colliding bubbles. At their intersection we found younger and smaller bubbles indicating active star formation. We propose that, by squeezing the interstellar material, collisions of bubbles increase the probability of further star formation. We find that the expansion and collision of bubbles appear to be important mechanisms facilitating star formation in our Galaxy.