Galaxies collide and stars grow very, very slowly. Astronomical timescales are massive, and it's rare that scientists can view dramatic changes in the sky. But such is the case with the image above: the first X-ray evidence of a supernova shock wave breaking through a cloud of gas around an exploded star.

160 million years ago, the supernova above -- located in the galaxy UGC 5189A -- exploded, and in early October 2010, the first rays of that explosion reached Earth. The Chandra X-ray Observatory, NASA's x-ray space telescope, captured the galaxy's image both in December 2010 and eleven months later, in October 2011. The Hubble Space Telescope also photographed the galaxy. The image above is a composite of all three: X-rays are shown in purple, overlaid on the Hubble's photograph of the visible spectrum.

Here's where the evidence comes from: SN 2010jl, which shines brightest with X-rays near the top of the galaxy. (Although there is another strong X-ray source, possibly a black hole, very close to it.) When observed in December, SN 2010jl's X-rays were mostly absorbed by the supernova's surrounding "cocoon" of gas. In the second -- eleven months later -- the supernova's incredibly hot gas has scattered X-rays beyond the cocoon. A noticeable change in two different observations, and evidence that a supernova's energy breaks through its gas cocoon.

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