The Crab Nebula is famous for being the remnants of a supernova that occurred in 1056 CE. Almost seven thousand years ago (as the nebula is six thousand light years away), a star finished off the last of its fuel, and the competing forces of gravity and the nuclear fusion reaction suddenly became a very one-sided competition, blowing the outer layers of the star out into space. Gravity won out for the majority of the mass, and collapsed into an extremely dense pulsar — something the mass of our Sun but the size of a small town, that spins about thirty times a second. Those outer layers that it cast out, have been expanding steadily over the last thousand years (well, again, seven thousand, but we can’t yet see what they look like today because they’re so far away).
The retrofitted Hubble got this amazing shot. Click it to go to the original, super-high-res photo.
Hat tip to Astronomy Picture of the Day.