Much has been learned about stars by studying their infrared emission. Infrared observations have led to the discovery of a large number of stars which are too cool to be detected by their visible light or are hidden behind obscuring dust. Infrared observations have also led to the discovery of several stars which have orbiting material.

Above is an image of infrared point sources in the entire sky as seen by the Infrared Astronomical Satellite (IRAS). The plane of our Galaxy runs horizontally across the image. Sources are color coded by their infrared colors. Blue sources are cool stars within our Galaxy, which show an obvious concentration to the galactic plane and center. Yellow-green sources are galaxies which are basically uniformly distributed across the sky, but show an enhancement along a great circle above the galactic plane. This enhancement is caused by galaxies in the Local Supercluster. Reddish sources, the infrared cirrus, are extremely cold material close to us in our own Galaxy. Black areas were not surveyed by IRAS.

In 1997, the infrared camera on the Hubble Space Telescope (NICMOS) revealed one of the brightest stars in our galaxy. This star, which is 10 million times more radiant than our Sun, was discovered in the center of our galaxy where it was hidden from visible light telescopes by thick dust. In the image you can see two expanding shells of gas being ejected by the star in one of the largest stellar eruptions ever seen.
Don F. Figer (UCLA) and

U.C. Berkeley Space Sciences
Laboratory/W.M. Keck Observatory
The image to the left shows a "spiral" star which was discovered in the infrared. The star (Wolf-Rayet 104) is 3 times the size of our sun and 100,000 times brighter. Because it is so large and radiates so intensely, part of its outer atmosphere is being blown off. Wolf-Rayet 104 is a binary star system - its companion is a smaller OB star. The material being ejected from Wolf-Rayet 104 is swept into a spiral pattern by the stellar winds of both stars.
Stars are often form in groups called star clusters. The stars in a cluster will usually move slowly away from each other as they age. Many new star clusters are still partially hidden by the dust and gas leftover from star formation, making them more difficult to view in visible light. Infrared light, however, can penetrate this dust and provide us with a deeper view of the cluster. The image to the right is an infrared view of the Quintuplet Star Cluster which lies near the center of our Milky Way Galaxy. Since the center of our galaxy is a very dusty place, infrared observations are often the best way to view objects embedded in and hidden by this dust. This image taken with the NICMOS instrument on the Hubble Space Telescope is the clearest view yet of this cluster.

Don Figer (STScI) et al., NASA

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