A cloud of gas

The story begins in interstellar space: a wave propagates through the gas (possibly caused by the explosion of a nearby supernova ^? ) and a part of the cloud begins to contract.

The cloud collapses, the density and temperature increase at its centre. As it becomes smaller, the cloud begins to rotate on its axis and takes the form of a disk surrounding a central mass.

What happens next will depend on the quantity of matter present in the central mass...