In 185 A.D., Chinese astronomers saw a strange "guest star" suddenly appear in the night sky. It was visible for a staggering eight months. That was enough time for ancient skywatchers to take notice and make the first-known observation of a supernova in human history. There’s also some evidence that Roman astronomers witnessed the event.
In modern times, astronomers have rediscovered the remains of this dead star. Their studies have revealed that Supernova RCW 86 happened after a neighboring star offloaded huge amounts of its own matter onto a white dwarf, which is essentially a stellar corpse. This led to what astronomers call a Type Ia supernova that exploded some 8,000 light-years from Earth.
Above, combined X-ray images from NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton Observatory show how a shockwave heated the interstellar gas to millions of degrees.
Supernova G347.3-0.5. (Credit: Chandra: NASA/CXC/SAO/P.Slane et al.; XMM-Newton: ...
