Stars produce energy from nuclear reactions, primarily the fusion of hydrogen to form helium.

Infrared astronomy is a natural tool to use in studying star formation because infrared light penetrates the surrounding dust and be— cause protostars are expected to emit infrared light. Because of these facts, infrared observations have been the primary means used to search for stars in the process of formation.

Turbulence helps initiate the formation of stars, which feeds material and energy back into the ISM and drives further turbulence. But large-scale dynamical processes, such as the shear induced by galactic rotation and the accretion of gas from outside the galaxy, also drive turbulence.

A shock wave will cause the molecular cloud to collapse. The shock wave could either be from a violent event, like a supernova, or the stellar winds from young stars compressing the gas around them. What is the source of energy in a protostar?

Shrinking gas clouds heat up because the gravitational potential energy of gas particles far from the cloud center is converted into thermal energy as the gas moves inward.

Which two processes can generate energy to help a star or gas cloud maintain its internal thermal pressure? Which process is required to allow a gravitationally-collapsing gas cloud to continue to collapse? The cloud must radiate away much of its thermal energy.

Under the influence of its own gravity, the nebula contracts. As it contracts, it spins faster and faster, much like an ice skater who pulls in her arms. As it continues to flatten and spin, the nebula becomes denser and hotter, particularly in the center.