STARBIRTH

New stars are born out of dense gas clouds. Gravitational forces (contraction) must overcome gas pressure (expansion) in order for this to occur.

As the clouds contracts, it heats up, and the dust grains in the outer portions emit infrared radiation. Thus, we see these "protostars" best in the infrared.

The inner portion of the cloud collapses until pressure re-establishes the balance once nuclear reactions begin in the core ... "a star is born"!

The outer portions continue to rain in on the newborn star, and some of this material ends up in a disk surrounding the star. The disk is probably responsible for bipolar outflows (oppositely directed jets of material) that are seen in young stars.

The disk material forms the basic mass for the eventual creation of planets orbiting the star. That disks are often found around young stars indicates that planetary systems may be common around other stars.