Just as the microscope revolutionized the study of the human body by revealing the workings of cells, the Hubble Space Telescope is offering astronomers an unprecedented look at fine structure within these shock fronts. Astronomers have been performing calculations of what should go on behind shock fronts for about the last 20 years, but detailed observations have not been possible until Hubble.
This image was taken with Hubble's Wide Field and Planetary Camera 2 (WFPC2). The color is produced by composite of three different images. Blue shows emission from "doubly ionized" oxygen atoms (atoms that have had two electrons stripped away) produced by the heat behind the shock front. Red shows light given off by "singly ionized" sulfur atoms (sulfur atoms that are missing a single electron). This sulfur emission arises well behind the shock front, in gas that has had a chance to cool since the passage of the shock. Green shows light emitted by hydrogen atoms. Much of the hydrogen emission comes from an extremely thin zone (only several times the distance between the Sun and Earth) immediately behind the shock front itself. These thin regions appear as sharp, green, filaments in the image.
Credit: Jeff Hester (Arizona State University) and NASA
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