Question

How are stars formed?

Since stars are made of gas, the Milky Way is Galaxy is a good place to start looking for where the youngest stars reside. The Milky Way Galaxy is a giant molecular cloud that is a reservoir of gas and dust. Molecular clouds are not smooth, but rather contain clumps or dense cores of material with low temperatures and densities much higher than is typical of most of the rest of the cloud. Both of these conditions-low temperature and high density- are just what is required to male new stars. In order to form a star-that is, a dense, hot ball of matter capable of starting nuclear reactions deep within-we need a massive clump of atoms and molecules to shrink in radius and increase in density by a factor of nearly 10 20. Such a drastic collapse is brought about by the force of gravity. The essence of the star's life story is the ongoing competition between two forces: gravity and pressure. The force of gravity, pulling inward, tries to make a star collapse. Internal pressure produced by the motions of the gas atoms, pushing outward, tried to force the star to expand. When these two forces balance, the star is stable. Major changes in the structure of a star occur when one or the other of these two forces gains the upper hand. When a star is first forming, low temperature and high density both work to give gravity the advantage.
December 11, 2001