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This close-up of the Cygnus Loop shows the shock wave from a supernova that took place 15,000 years ago striking and heating interstellar gas and dust. The green filaments indicate hot hydrogen atoms just behind the shock front. Blue represents somewhat cooler oxygen atoms farther behind the shock front. Red comes from sulfur atoms well behind the shock front. These have had time to cool considerably compared to the others. This image clearly indicates how the expanding blast becomes distorted by its passage through regions of space containing different amounts of gas and dust. Image credit: Hubble Space Telescope; The main source for HST images and explanations is HubbleSite.org. |
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