When a star like the Sun dies, it blows material off into space. Once that outer layers of the star are sloughed off, the hot dense core can light that gas up until it glows. The hydrogen emits red, the oxygen green and blue... these so-called planetary nebulae are some of the most elegant and beautiful objects in the sky.
Among the most famous of them is NGC 6543, the Cat's Eye Nebula, named for the shape of the central region; it does resemble the eye of a cat. But in this very deep exposure taken using 2.5 meter Isaac Newton Telescope on the island of La Palma in the Canaries, we're seeing much more than that. It reveals the far fainter outer material, shed millennia ago by the star. This outer halo is pretty big: 6 light years across! Most planetary nebulae are only a light year or so across, so this is a fantastically vast and gossamer structure.
The knots and clumps are where the expanding gas encountered material between the stars, compressing it and forming those tendrils. Giant halos around planetaries are hard to observe because they're so faint, but several have been seen. They're like the preserved remnants of an ancient star, and examining them is like doing astronomical archaeology... on a scale 60 trillion kilometers (40 trillion miles) across.
Image credit: This image was obtained and processed by members of the IAC astrophotography group (A. Oscoz, D. López, P. Rodríguez-Gil and L. Chinarro).