The nebula is surrounded by a vast halo of matter about 3 light years wide. This halo is probably formed by the gas expelled by the star before becoming a white dwarf.
This image, which instead shows the central nebula, was created by combining the data obtained in visible light from the Hubble telescope and in x-rays from the Chandra telescope.
Observations showed that the structure of the Cat's Eye is bipolar and symmetrical. The mechanisms that led to the formation of such a regular structure are not yet known.
It has been supposed that at the center of the nebula there is a binary system of stars, one of which is a white dwarf surrounded by an accretion disk. In this way it would be possible to explain the two polar jets which, interacting with the gas of the nebula, create the two most elongated parts in opposite directions.
To explain the various irregular bubble-shaped shells surrounding the central system, it was supposed that the white dwarf did not eject all its surface layers at the same time, but at different instants.
However, there is still no explanation for the concentric circles separated by regular distances visible outside the brightest part of the nebula. Their conformation suggests that they were produced by regular phenomena over time and with a similar emission speed, but the mechanism behind them remains unknown today.
Credit: NASA, ESA, Hubble Legacy Archive; Chandra X-ray Obs, Rudy Pohl.
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