Stars form within the densest parts of great gatherings of
gas and dust known as molecular clouds.
The first stage in the process of stellar birth involves the formation of
a distinct clump within such a cloud. The clump becomes detached from its
surroundings and begins to contract under its own gravitational pull. At
the center of the collapsing cloud, where the density is greatest, a protostellar
core forms. Over a period of about a million years this core draws in
more and more material from its surroundings until it achieves the status
of a protostar. After a further period,
the protostar evolves to become a pre-main-sequence
object such as a T Tauri star.
|A star-forming region, 1,000 light-years away in
Aquila. About 100 protostars have been found in this stellar nursery,
together with 600 other objects that will eventually pass throught
the protostar stage.