Cat's Eye Nebula - Kinematics and Morphology

Kinematics and Morphology

The Cat's Eye Nebula is structurally a very complex nebula, and the mechanism or mechanisms that have given rise to its complicated morphology are not well understood. The central bright part of the nebular consists of the inner elongated bubble (inner ellipse) filled with hot gas. It in turn is nested into a pair of larger spherical bubbles conjoined together along their waist. The waist is observed as the second larger ellipse lying perpendicular to the bubble with hot gas.

The structure of the bright portion of the nebula is primarily caused by the interaction of a fast stellar wind being emitted by the central star with material ejected during the formation of the nebula. This interaction causes the emission of X-rays discussed above. The stellar wind, blowing with the velocity as high as 1900 km/s, has 'hollowed out' the inner bubble of the nebula, and appears to have burst the bubble at both ends.

It is also suspected that the central star of the nebula may be a binary star. The existence of an accretion disk caused by mass transfer between the two components of the system may give rise to polar jets, which would interact with previously ejected material. Over time, the direction of the polar jets would vary due to precession.

Outside the bright inner portion of the nebula, there are a series of concentric rings, thought to have been ejected before the formation of the planetary nebula, while the star was on the asymptotic giant branch of the Hertzsprung-Russell diagram. These rings are very evenly spaced, suggesting that the mechanism responsible for their formation ejected them at very regular intervals and at very similar speeds. The total mass of the rings is about 0.1 solar masses. The pulsations that formed the rings probably started 15,000 years ago and ceased about 1,000 years ago, when the formation of the bright central part began (see above).

Further out, a large faint halo extends to large distances from the star. The halo again predates the formation of the main nebula. The mass of the halo is estimated as 0.26–0.92 solar masses.