The Cat’s Eye Nebula

NGC 6543 or the Cat’s Eye Nebula, discovered by William Herschel on February 15, 1786, is a relatively bright 8.1 magnitude planetary nebula in the constellation of Draco, situated almost exactly in the direction of the North Ecliptic Pole. The Nebula lies 3,000 light-years from Earth.

Structurally, it is one of the most complex nebulae known, with high-resolution image from Hubble’s Advanced Camera for Surveys (ACS) showing a bull’s eye pattern of eleven or even more concentric rings, or shells, around the Cat’s Eye. Each ‘ring’ is actually the edge of a spherical bubble seen projected onto the sky, that’s why it appears bright along its outer edge. Observations suggest the star ejected its mass in a series of pulses at 1,500-year intervals. These convulsions created dust shells, each of which contain as much mass as all of the planets in our solar system combined (still only one percent of the Sun’s mass). These concentric shells make a layered, onion-skin structure around the dying star. The view from Hubble is like seeing an onion cut in half, where each skin layer is discernible.

In the center of the Cat’s Eye there is a bright and hot star; around 1000 years ago, this star lost its outer envelope, producing the nebula. The main body has a temperature of about 7,000–9,000 K, whereas the outer halo has a higher temperature of about 15,000 K.

Infrared Image

These colour pictures below, taken with the Wide Field Planetary Camera-2, is a composite of three images taken at different wavelengths. (red, hydrogen-alpha; blue, neutral oxygen, 6300 angstroms; green, ionized nitrogen, 6584 angstroms). The image was taken on September 18, 1994.

A preliminary interpretation suggests that the star might be a double-star system. The dynamical effects of two stars orbiting one another most easily explains the intricate structures, which are much more complicated than features seen in most planetary nebulae. The two stars are too close together to be individually resolved by Hubble, and instead, appear as a single point of light at the center of the nebula.

An optical Image of the Nebula’s Surrounding Halo. An enormous but extremely faint halo of gaseous material surrounds the Cat’s Eye Nebula and is over three light-years across. Within the past years some planetary nebulae been found to have halos like this one, likely formed of material ejected during earlier active episodes in the star’s evolution.