Exact definition of young stars and their protoplanetary disks

Imagine that you go in the middle of night in dense, dense fog and see in the distance flickering areas of light from cars and the cities. It is almost impossible to define where there are fires - in the depth of fog or beyond its limits. The astronomers, trying to find young stars, face a similar problem: the stellar light for which they hunt, flickers through huge areas of foggy gas and a dust in space, called by molecular clouds. But the internal maintenance of these clouds often are a nutrient medium for young stars and planets - an ideal place to try to find out how...