Home
The Paths of Stars
A star begins its life as part of the interstellar medium, usually as a dense core in a giant molecular cloud. If something (like a nearby supernova or a spiral density wave) can compress this cloud core some, it will begin to collapse under its own gravity. Most of the mass will quickly settle in the center of the cloud core while the envelope slowly falls inward. At this stage, astronomers refer to the source as a protostar. Because of its very cold temperature, astronomers must look in the far infrared or at millimeter wavelengths to see it. At visual wavelengths, protostars are completely dark.
Protostars continue to contract gravitationally while material continues to accrete onto their surface. As they contract, their temperature rises, making them visible first in the infrared and eventually as star-like objects in the visual. Usually, these young stars are embedded within the clouds from which they formed, making them difficult to see in the optical.
They often form in large groups with much more massive stars. In these stellar nurseries, the massive stars destroy the material around them, producing beautiful ionized nebulae.
Last modified 19 September, 2002. © Gregory C. Sloan.