Resolving a Galaxy

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Two recently released images of the Small Magellanic Cloud, a small companion galaxy to our own, illustrate how new space-borne observatories are making it possible for astronomers to discern distant galaxies with ever greater clarity. These "first light" images were captured by instruments aboard the Midcourse Space Experiment (MSX) -- a Ballistic Missile Defense Organization satellite launched in April--that recorded radiation from the Small Magellanic Cloud in the infrared and ultraviolet wavelengths. The images display at least a five-fold improvement in resolution and sensitivity over those from previous experiments.

The infrared spectral region is ideal for observing cool sources and objects enshrouded in dust. The image above, was until now the best infrared view of the SMC. It contains four bright sources, two of which are part of extended infrared-emitting regions in the densest part of the galaxy.

This is the same view recorded by the new MSX Spatial Infrared Imaging Telescope (SPIRIT III), built by the Space Dynamics Laboratory of Utah State University. Here, the diffuse area is resolved into a rhomboid-shaped group of clearly defined sources.

This is a visible-light image taken by an optical telescope at Mt. Palomar, Calif. The Small Magellanic Cloud appears as the faint semi-elliptical patch in the center. The fuzzy appearance is due to the high concentration of ordinary stars of similar brightness scattered throughout the galaxy.

Here is an image of the same region, captured by the MSX Ultraviolet Visible Imagers and Spectrographic Imagers (UVISI), which were built by The Johns Hopkins University Applied Physics Laboratory. The ultraviolet rays originate primarily from very hot stars, those with surface temperatures in excess of 15,000 kelvins, and nebulae irradiated by such stars. Many of the sources seen in the visible-light image at left are easily identifiable in the UVISI image. The major difference lies in the prominence given by UVISI to hot gas and stars.

Photo Credit: THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY

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