A ROSAT PSPC all-sky survey image of the nearby supernova remnant (or stellar wind bubble) Loop 1, powered by the Sco OB associations. OB associations are groups of young, very bright, and very large stars. The radiation pressure these bright stars produce is able to heat up the gas and dust that normally lies between stars, and push it farther from the center of the group into a glowing bubble or shell around the association.
The color-coded image of the X-rays indicates the hardness of the X-rays, where red is soft and blue is hard.
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