Star Formation

Stars form from collapsing clouds of gas and dust. As the cloud collapses, its density and temperature increase. The temperature and density are highest at the center of the cloud, where a new star will eventually form. The object that is formed at the center of a collapsing cloud, and which will become a star, is called a protostar. Since a protostar is embedded in a cloud of gas and dust, it is difficult to detect in visible light. Any visible light that the protostar emits is absorbed by the material surrounding it. Only during the later stages, when a protostar is hot enough for its radiation to blow away most of the material surrounding it, can it be seen in visible light. Until then, a protostar can be detected only in the infrared.

IRAS images of star forming regions in Orion and Rho Ophiuchi

The light from a protostar is absorbed by the dust surrounding it, causing the dust to warm up and radiate in the infrared. Infrared studies of star forming regions give us important information about how stars are born, and thus, on how our own Sun and solar system were formed. The first infrared observatory sent into space, IRAS cataloged thousands of hot, dense cores within clouds of gas and dust which could be newly forming stars.

To the right is an infrared image of the Kleinmann-Low Nebula, a region of intense star formation in the constellation Orion. In visible light much of this region is hidden by dust however in the infrared you can see the effects of the hot winds produced by newly formed massive stars. These hot winds heat up the surrounding gas and cause them to radiate strongly in the infrared. The winds will eventually clear much of the gas and dust surrounding the stars.

CISCO, Subaru 8.3-m Telescope, NAOJ

C. Robert O'Dell, Shui Kwan Wong (Rice Univ),NASA
and R. Thompson (U. Arizona) et al., NASA

Here is a comparison of a visible light (left) and an infrared (right) view of OMC-1 (OMC stands for Orion Molecular Cloud) taken by the Hubble Space Telescope. In this region of active star formation you can clearly see the benefits of observing in the infrared. The visible light image does not show many features because optical telescopes cannot see past the thick areas of dust and gas in which new stars are formed. By contrast, in the infrared we can "see" past the dust. The infrared image shows stars and glowing interstellar dust heated by the intense starlight of the newborn stars.

Stars are born within cocoons of dust and dense molecular gas, and are mostly hidden from view at visible wavelengths. Near-infrared light, at wavelengths of a few microns, can pierce through the dusty veil to provide astronomers with a peek at a newborn star. The Spitzer Space Telescope will use its short-wavelength camera to probe the formation and early evolution of young stellar objects in the first million years of their life. Spitzer observations will also reveal the extent to which new stars are formed in clusters, rather than in isolation.