DR RUDOLPH SCHILD / SCIENCE PHOTO LIBRARY DR RUDOLPH SCHILD / SCIENCE PHOTO LIBRARY
Optical CCD image of the barred spiral galaxy M109 (NGC 3992). The image shows clearly the different types of stellar populations between the bar and the arms of the galaxy. The bar together with the nucleus is dominated by old yellow stars, such as our Sun, while the spiral arms are populated by much bluer and younger stars. Several blue knots are also visible in the arms. They represent denser associations of young stars which have ionised the surrounding clouds of hydrogen. The image was obtained with blue-green, red and near infrared filters and it may be considered a true colour version.
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