The explosions of dying stars, known as supernovas, are some of the most powerful events in our entire universe, releasing more energy than the Sun will in its entire 10-billion-year lifetime. (The Sun is no small player, either—it produces the energy of nearly a trillion 1 megaton bombs every 10 seconds.)
The sheer power of a supernova explosion is enough to blast out debris at speeds of around 20 million miles per hour, generating shockwaves – pressure wavefronts that move faster than the speed of sound as they collide with surrounding gas and dust. As the shockwaves radiate outward into space, they dramatically heat this material up to temperatures of tens of millions of degrees, causing the supernova remnant to glow in X-rays.
Such immense, swift forces may seem completely unstoppable, but in the case of one supernova remnant in our Galaxy, G21.5-0.9, images from NASA's Chandra X-ray Observatory reveal that a mysterious presence was able to stop G21.5-0.9's shockwaves in their tracks.
Supernova remnant G21.5-0.9
(Credit: NASA/CXC/U.Manitoba/H.Matheson & S.Safi-Harb)