STAR FORMATION

Many of the most interesting infrared objects are associated with 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 the 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 it does emit 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. The light from the 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 will give us important information about how stars are born and thus on how our own Sun and Solar System were formed.

Infrared telescopes have cataloged thousands of hot, dense cores within clouds of gas and dust which could be newly forming stars. To the right are two infrared images of star forming regions: an IRAS view of the constellation Orion in which there are several regions active star formation, and an image from the new Spitzer Space Telescope of newborn stars in the nebula NGC 7129.

IRAS image of Orion (left) and Spitzer image of NGC 7129 (right)

Laird Close, University of Hawaii

Protostars which are starting to blow away the gas and dust surrounding them are called T-Tauri stars. The warm dust remaining around T-Tauri stars still radiates in the infrared. There is evidence that the remaining dust and gas surrounding T-Tauri stars form rotating disks which may mark the beginnings of planetary systems. Herbig-Haro objects, which are also associated with newly forming stars, can be studied in the infrared. These are small nebulae which vary in shape and brightness over a period of only a few years. Both Herbig-Haro objects and T-Tauri stars are found in regions of active star formation. It is thought that these nebulae represent high speed gas flowing from young stars colliding with interstellar clouds. The study of T-Tauri stars and Herbig-Haro objects will help us understand the details on how stars are formed. To the left s an infrared adaptive optics image of a T-Tauri stars (UY Aur).

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 University),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.

Globules are also found in star forming regions. These are small clouds (~ 1 light year in diameter) which contain 10 to 1000 solar masses of gas and dust. In visible light, globules are seen in dark silhouette against bright nebulae. They produce no visible light of their own and are thought to be collapsing clouds which will produce stars. Infrared observations from IRAS showed that some globules contain protostars. To the right is an infrared image of the globule in the nebula IC 1396 taken by the new Spitzer Space Telescope. Spitzer's sensitive infrared detectors unveiled the brilliant hidden interior of this opaque cloud of gas and dust and revealed, for the first time, a glowing stellar nursery with never-before-seen young stars and stars still in the process of formation. The inset shows a visible light view of the same region.

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