What is a shock compressed molecular cloud?

Molecular clouds are aggregations of rarefied gas (mainly hydrogen) from which stars can form. Often the impetus for star formation is an energetic shock wave from a nearby cosmic event such as a supernova. This compresses the gas along the shock front, causing it to clump. A situation of positive feedback can ensue, the clump becoming more massive, thus having a larger gravitational attraction (since gravity depends on mass). This increased attraction draws more material in, thus increasing the mass...