A rippling bubble of gas marks the aftermath of a supernova explosion in the Large Magellanic Cloud, a companion galaxy to the Milky Way, in this Hubble Space Telescope image. Recent research suggests the explosion was triggered by the collision of two white dwarf stars, which are the dead cores of once-normal stars like the Sun. The bubble, known as SNR 0509-67.5, is about 23 light-years in diameter and is expanding at 11 million miles per hour. [NASA/ESA/Hubble Heritage Team (STScI/AURA)]