Back in 2002 an astronomer using the Nordic Optical Telescope was studying a planetary nebula called the “Cat’s Eye.” To backyard scopes it appears like a complex-looking little puff of light and in fact, is a difficult object to find unless you have a pretty decent scope. Scientists like to study these nebulae for a number of reasons — for one thing, they give us a good idea of how our own Sun might die in a few billion years. For another, these ancient stars are putting out tremendous amounts of material into the interstellar medium — stuff which eventually will end up in the birthplaces of future stars and maybe even a few planets.
As these stars age, they puff off their outer atmospheres, forming a bubble of gas and dust in surrounding space. Eventually the radiation from the star lights up the outrushing debris, and sometimes the influence of a companion star, or a magnetic field, or a fast, hot jet of gases from the dying star, will sculpt the cloud into fantastic shapes. The Cat’s Eye is a cavern of gas and dust surrounding an ancient star and possibly a nearby companion. The interactions have shaped the surrounding materials and the star’s emissions have turned the whole sight into a glowing “cave” structure.
This fantastic picture shows various gases lit up by the star. Here’s how the scientist who did the observation — Romano Corradi — explains the colors:
“I put in green and blue for the ionized oxygen emission; I used two colours for a single emission line because of the large dynamical range of the nebula+halo (there is a contrast of 1 million between the faintest and brightest structures detected), and I wanted to display the three different components of the nebula, i.e. inner nebula, first halo with the (in blue) rings, and outer filamentary halo. Red is instead [NII]6583. The image is the deepest ever obtained of NGC 6543.”
A few years ago the Hubble Space Telescope studied the inner portion of the Cat’s Eye — the “marble” surrounded by loopy looking structures at the center of this image. They, too, color-coded the image to map the different kinds of emissions put out by the clouds. This “astro-chemical” analysis tells astronomers a great deal about the age of the star, the layers of its atmosphere it has lost, and what kinds of elements are being returned to space for the next generation of stars and planets.
