The aftermaths of supernovae always produce X-rays, but if the supernova’s blast wave strikes dense surrounding gas, it can produce a particularly large dose of X-rays that arrives months to years after the explosion and may last for decades, according to X-ray observations of 31 supernovae and their aftermath obtained from NASA’s Chandra X-ray Observatory, NASA’s Swift and NuSTAR missions, and ESA’s XMM-Newton X-ray observatory. This threat...
