At such low temperatures, gases start to group together densely like molecules, usually in the form of carbon monoxide and H2. When the density reaches a certain point, the cloud core - which is denser than the outer cloud - collapses under its own weight, due to gravity.
As the core collapses, it fragments into clumps, which then forms into a protostar. All of this happens over the course of around 10 million years.
So how did the crystals get there? A new paper in Astrophysical Journal Letters suggests that jets of gas are responsible, shooting away from the star about to be born. The crystals form near the surface of the protostar, then are carried into the surrounding cloud by the jets, where they cool and then fall back down onto the protostar like tiny bits of glitter.
It would be quite a sight, apparently, from the view inside the core cloud. "If you could somehow transport yourself inside this protostar's collapsing gas cloud, it would be very dark," says lead author Charles Poteet (University of Toledo) in NASA's official press release. "But the tiny crystals might catch whatever light is present, resulting in a green sparkle against a black, dusty backdrop."