Our galaxy has numerous large, dark quiescent gas and dust clouds where there is no sign of star formation taking place. It seems that some external force is needed to trigger star formation. There are a number of plausible sources for such a force such as shocks from colliding clouds, expanding HII regions, a passing star's gravitational field or the shockwave from a supernova are probably some of the most likely. In any case once a local density enhancement has been formed this slightly denser region will tend to attract gas and dust from surrounding regions due to it having a slightly larger gravitational field. As it attracts more gas and dust the mass and density of the region will increase, further enhancing its gravitational field and thus attracting more gas and dust. This process may repeat itself in many different parts of the cloud, thus forming numerous clumps. Clearly the initial stages of this process cannot be seen from the Earth as the initial density fluctuations are too small to be seen. However, the later stages are certainly observable and there are numerous examples of gas clouds with many clumps within them that are not yet hot enough to be thought of as protostars (the Orion cloud is just one place where such examples can be found).