Hubble Heritage Archive: The Cat’s Eye Nebula, NGC 6543

The text and images in this article were originally published on September 9, 2004, and reflect information about NGC 6543 available at that time.


In this detailed view from NASA’s Hubble Space Telescope, the so-called Cat’s Eye Nebula looks like the penetrating eye of the disembodied sorcerer Sauron from the film adaptation of The Lord of the Rings.

The nebula, formally catalogued NGC 6543, is every bit as inscrutable as the J.R.R. Tolkien phantom character. Though the Cat’s Eye Nebula was the first planetary nebula to be discovered, it is one of the most complex such nebulas seen in space. A planetary nebula forms when Sun-like stars gently eject their outer gaseous layers that form bright nebulas with amazing and confounding shapes.

In 1994, Hubble first revealed NGC 6543’s surprisingly intricate structures, including concentric gas shells, jets of high-speed gas, and unusual shock-induced knots of gas.

As if the Cat’s Eye itself isn’t spectacular enough, this new image taken with Hubble’s Advanced Camera for Surveys (ACS) reveals the full beauty of 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.

Until recently, it was thought that such shells around planetary nebulas were a rare phenomenon. However, Romano Corradi (Isaac Newton Group of Telescopes, Spain) and collaborators, in a paper published in the European journal Astronomy and Astrophysics in April 2004, have instead shown that the formation of these rings is likely to be the rule rather than the exception.

The bull’s-eye patterns seen around planetary nebulas come as a surprise to astronomers because they had no expectation of episodes of mass loss at the end of stellar lives that repeat every 1,500 years. Several explanations have been proposed, including cycles of magnetic activity somewhat similar to our own Sun’s sunspot cycle, the action of companion stars orbiting around the dying star, and stellar pulsations. Another school of thought is that the material is ejected smoothly from the star, and the rings are created later on due to formation of waves in the out-flowing material. It will take further observations and more theoretical studies to decide between these and other possible explanations.

Approximately 1,000 years ago the pattern of mass loss suddenly changed, and the Cat’s Eye Nebula started forming inside the dusty shells. It has been expanding ever since, as discernible in comparing Hubble images taken in 1994, 1997, 2000, and 2002. The puzzle is what caused this dramatic change? Many aspects of the process that leads a star to lose its gaseous envelope are still poorly known, and the study of planetary nebulas is one of the few ways to recover information about these last few thousand years in the life of a Sun-like star.

Featured Image Credit: NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA) Acknowledgment: R. Corradi (Isaac Newton Group of Telescopes, Spain) and Z. Tsvetanov (NASA)

Fast Facts about NGC 6543

About this Object

Object Name: Cat’s Eye Nebula, NGC 6543
Object Description: Planetary Nebula
Position (J2000): R.A. 17h 58m 33s.42
Dec. +66° 37′ 59″.5
Constellation: Draco
Distance: 3,000 light-years (1,000 parsecs)
Dimensions: This image is 1.2 arcminutes (1.2 light-years or 0.35 parsecs) wide

About the Data

Data Description: This image was created from HST observations from the following proposal: 9026: Z. Tsvetanov (JHU)
Instrument: ACS/WFC 
Exposure Date: May 4, 2002
Exposure Time: 1.2 hours
Filters: F502N [O III], FR505N [O III] and F658N (Halpha+[N II])

About this Image

Image Credit: NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA)
Release Date: September 9, 2004

Different Filters, Different Telescopes, 
Same Beautiful Planetary Nebula

NGC 6543, Cat’s Eye Nebula Imaged with Hubble
Credits: (left) NASA, ESA, J.P. Harrington and K.J. Borkowski (U. Maryland)
(right) NASA, STScI, and Z. Levay

These two images of the Cat’s Eye Nebula were both taken with the Hubble Space Telescope. The image on the left was taken in 1994 with the Wide Field Planetary Camera 2 (WFPC2) in filters that isolate hydrogen, oxygen, and nitrogen. The image on the right uses a sulfur filter taken with WFPC2 and combines it with hydrogen and oxygen filters taken in 2002 with the Advanced Camera for Surveys High Resolution Camera (ACS/HRC). (Note: the red line in the image on the right is an artifact of the HRC “occulting finger” used to block out starlight on bright sources.)

NGC 6543, Cat’s Eye Nebula Imaged with NOT
Credits: (left) R. Corradi (Isaac Newton Group) and D. Goncalves (Inst. Astrofisica de Canarias)
(right) Nordic Optical Telescope and R. Corradi (Isaac Newton Group of Telescopes, Spain)

The next two images are also of the Cat’s Eye Nebula, taken with the ground-based Nordic Optical Telescope (NOT), located on the island of La Palma, in the Canary Islands. Notice that the wide field of view of the ground-based telescope shows nebulosity out beyond the central region that was imaged by Hubble. Both images were taken by astronomer, Romano Corradi, in two narrow-band filters: nitrogen and oxygen. The images differ in the assignment of the color scheme used to show the differing filters. The left image shows nitrogen in red and oxygen in green and blue shades. The right image shows oxygen in blue and nitrogen in red.

Additional Images

HST* ACS (Detail)

HST* ACS (Full-field)


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