Figure A
Click on the image for larger version

The Blue Ring Nebula was discovered in 2004 by NASA's Galaxy Evolution Explorer (GALEX) mission. Astronomers think the nebula was created by the merger of two stars, and that we are seeing the system a few thousand years after the merger, when evidence of the collision is still apparent.

The blue light in the image shows the debris cloud created by the merger. As the hot cloud of material expanded into space and cooled down, it formed hydrogen molecules that collided with the interstellar medium (the particles occupying the space between stars). These collisions caused the hydrogen molecules to radiate far-ultraviolet light, which was detected by GALEX. Yellow indicates near-ultraviolet light, also detected by GALEX, which is emitted by the star at the center of the nebula and many surrounding stars.

Infrared light observed by NASA's Wide-field Infrared Survey Explorer (WISE) is also shown in red, and is primarily emitted by the central star. Detailed analysis of the WISE data revealed a ring of debris around the star – further evidence of a merger.

Magenta indicates optical light — light visible to the human eye — collected using the Hale Telescope. This light comes from the shockwave at the front of the expanding debris cones. The optical light helped astronomers discover that the nebula actually consists of two cones moving away from the central star. The base of one cone is moving almost directly toward Earth, while the other is moving almost directly away, and the magenta light outlines the two bases. The blue region in the image shows where the cones overlap; the non-overlapping regions are too faint for GALEX to see. Figure A shows the orientation of the cones to Earth and the way they appear to overlap.

Click here to see an animation of the geometry of the expanding gas cloud.

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. JPL also managed the Spitzer and WISE missions. In Sept. 2013, NASA reactivated the WISE spacecraft with the primary goal of scanning for near-Earth objects, or NEOs, and the mission and spacecraft were renamed NEOWISE.