A compression wave, or shock, can produce localized regions of high density which may then collapse under their own gravity. A flattened spinning disk of gas and dust is formed, with the material gradually moving to the centre of the disk to form a spherical core, called a protostar. As the core contracts it heats up. A new star is born if enough material accumulates in the core to turn on nuclear fusion, the process which provides the star's energy. Shocks in GMCs can be caused by two GMCs colliding, by the collision of two or more clumps within a GMC, or by a supernova explosion near or within the cloud.
Important questions concerning star formation remain unanswered.
These questions are difficult to answer observationally. A protostar is not as hot and bright as an ordinary star, and it is cocooned in the gas and dust that are still falling onto the spinning disk. Protostars are therefore hard to see from the Earth in visible light, although they can now be observed more easily due to recent advances in infra-red detector technology. Helen Pongracic and Sue Byleveld, a PhD student, are using numerical simulations to investigate the condensation of protostars out of interstellar clouds. This involves using a three-dimensional hydrodynamical code that incorporates gravity.