This gossamer ring in the sky may look as light and lovely as a soap bubble, but its appearance belies its unimaginably violent birth: The shell of reddish gas is actually the remnants of a supernova explosion riding a shock wave and ripping through space at more than 18 million kilometers per hour. The supernova remnant, dubbed SNR 0509, was first spotted by the Hubble Space Telescope in October 2006. This newly released picture combines data from that 4-year-old image, which was taken only at wavelengths that highlight glowing hydrogen, with a visible-light image snapped just last month. SNR 0509, which now appears to be about 23 light-years across, resides in the Large Magellanic Cloud, a galaxy about 160,000 light-years from Earth. When light from the supernova's distant explosion first reached Earth about 400 years ago, it could have outshone its parent galaxy for several days and was probably visible to the naked eye for months. However, there are no records of the event, which was visible from only the Southern Hemisphere.
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*This article has been corrected to note that the light from the explosion of SNR 0509 first reached Earth 400 years ago; previously, the article implied that the explosion itself occurred 400 years ago.