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The Blue Ring Nebula is thought to be the product of two stars merging into one. The collision of the bodies ejected a cloud of hot debris into space. A disk of gas orbiting the larger star cut the cloud in half, creating two cones that are moving away from the star in opposite directions.
The base of one cone is moving almost directly toward Earth, while the other is moving almost directly away. Magenta represents optical light from the shockwave at the front of the expanding debris cones, outlining the two cone bases at their widest points. Blue represents far-ultraviolet light (not visible to the human eye) and comes from gas behind the shockwave. As the gas expands and cools, it forms hydrogen molecules that interact with the interstellar medium and emit only far-ultraviolet light. These emissions are visible only where the cones overlap (as seen from Earth), forming the blue ring around the central star.
Figure A shows the orientation of the cones to Earth and the way they appear to overlap.
JPL, a division of Caltech, managed the GALEX mission for NASA's Science Mission Directorate. The mission was developed by NASA's Goddard Space Flight Center in Greenbelt, Maryland, under the Explorers Program.