The first portion of a galaxy to form is the galactic nucleus, which is the central core of the galaxy. The galactic nucleus is where the stellar density and the amount of interstellar matter is the highest. The nucleus also contains a supermassive black hole, which is thought to be the driving force behind the formation of the galaxy. The nucleus is formed from the collapse of a giant molecular cloud, which is a dense cloud of gas and dust that is the birthplace of stars. As the cloud collapses, it fragments into smaller and smaller pieces, until eventually a central core forms. This core is the nucleus of the galaxy.