Some nebulae are formed when a star explodes, in a huge, gigantic explosion... a supernova explosion. This explosion leaves behind a huge expanding cloud of gas, like the Crab Nebula, which is shown here. It looks a bit like a pile of glowing earthworms, doesn't it? A thousand years ago, way back in the year 1054 AD, a new, super-bright star appeared in the sky.
It was not actually a BRAND-NEW star, it was a faint star that had been there all along, and just suddenly got super-duper bright, and so became visible. When a star goes supernova, the core of the star collapses, and then `rebounds' outwards, throwing the outer layers of the star way out into space, created long, spaghetti-like filaments speeding through interstellar space.

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