Located 5,000 light years away in the constellation Gemini, this brain-shaped sphere of dust and gas is the visible remnant of a massive star that exploded as a supernova about 30,000 years ago.
Massive stars undergo a series of nuclear fusion reactions in their cores, creating heavier and heavier elements over time. The process starts with hydrogen burning into helium, followed by helium burning into carbon, which burns into oxygen, and so on, progressing through the elements up to iron. But fusing iron consumes more energy than it releases. As a result, once the core is mostly composed of iron, the star can no longer generate enough pressure to support itself against gravitational collapse.
The collapse happens very rapidly, and when the core reaches nuclear density, it bounces back, leading to an explosive release of energy. This expels the outer layers of the star, creating a supernova and leaving behind a dense neutron star or black hole. The nebula we see is formed by the neutron star’s blast wave, expanding into space and interacting with the surrounding molecular cloud.
