NASAのインスタグラム(nasagoddard) - 10月30日 06時00分

The Cat's Eye Nebula, one of the first planetary nebulae discovered, also has one of the most complex forms known to this kind of nebula. At least eleven rings, or shells, of gas encircle the center of the Cat's Eye.

The beauty of the Cat's Eye Nebula is revealed in this detailed view from @NASAHubble. The image from Hubble's Advanced Camera for Surveys (ACS) shows a bull's eye pattern of at least eleven 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 dying star that produced the Cat’s Eye 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 (which is 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.

The bull's-eye patterns seen around planetary nebulae come as a surprise to astronomers because they had no expectation that episodes of mass loss at the end of stellar lives would 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 the formation of waves in the outflowing material.

Credit: NASA, ESA, HEIC, and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: R. Corradi (Isaac Newton Group of Telescopes, Spain) and Z. Tsvetanov (NASA) #nasagoddard #spacecat #space #science #nationalcatday

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