Researchers have created the first computer-generated 3D model of the Cat’s Eye Nebula, revealing a pair of identical rings that surround the nebula’s outer crust. The symmetry of the rings indicates that they were formed by a prior jet, providing strong evidence for a binary star at the center of the nebula. The study was led by Ryan Claremont, who recently finished high school in the United States, and was published in Monthly Notices of the Royal Astronomical Society.
A planetary nebula forms when a dying solar-mass star ejects its outer layer of gas, creating the colorful, shell-like structure characteristic of these objects. The Cat’s Eye Nebula, also known as NGC 6543, is one of the most complex planetary nebulae known. It is just over 3,000 light-years from Earth, and can be seen in the constellation of Draco. The Cat’s Eye Nebula has also been imaged by the Hubble Space Telescope in high resolution, revealing a complex structure of knots, spherical shells, and arc-like filaments.
The nebula’s mysterious composition has baffled astrophysicists because it cannot be explained by previously accepted theories of planetary nebula formation. Recent research has shown that presynaptic jets were potential formation mechanisms in complex planetary nebulae such as NGC 6543, but they lack a detailed model.
Ryan Claremont, an avid astronomy enthusiast, decided to try creating a detailed 3D structure of a cat’s eye to learn more about the possible mechanism that gave it its complex shape. To do this, he sought help from Dr. Wolfgang Stephen of the National Autonomous University of Mexico and Nico Koning of the University of Calgary, who have developed a 3D astrophysical modeling program SHAPE particularly suited to planetary nebulae.
To reconstruct the 3D structure of the nebula, the researchers used spectroscopic data from the San Pedro Martír National Observatory in Mexico. These provide detailed information about the internal movement of material in the nebula. Combined with this data and images from the Hubble Space Telescope, Claremont created a new 3D model, confirming rings of high-density gas wrapped around the cat’s eye’s outer shell. Surprisingly, the rings are almost completely symmetrical to each other, which indicates that they were formed by a jet – a stream of high-density gas ejected in opposite directions from the nebula’s central star.
The jet exhibited forward motion, similar to the oscillating motion of a rotating top. As the plane swung, or advanced, I marked a circle, forming rings around the cat’s eye. However, the data indicate that the loops are only partial, meaning that the pre-jet never completed a full 360-degree rotation, and the appearance of the jets was merely a short-lived phenomenon. The duration of the outflows is an important piece of information for the theory of planetary nebulae. Since only binary stars can power a precursor jet in the planetary nebula, the team’s results are strong evidence for a system of this type at the center of the cat’s eye.
Because the angle and direction of the plane changed over time, it likely formed all of the features seen in a cat’s eye, including jets and knots. Using the 3D model, the researchers were able to calculate the tilt and open angle of the pre-jet based on the orientation of the rings.
“When I first saw the Cat’s Eye Nebula, I was struck by its beautiful, perfectly symmetrical structure. I was even more surprised that its three-dimensional structure was not completely understood,” says Ryan Claremont, lead author of the research paper and now a prospective undergraduate at Stanford University.
He adds, “It has been very rewarding to be able to do my own astrophysical research that has a real impact in this field. Jets in planetary nebulae are relatively rare, so it is important to understand how they contribute to the formation of more complex systems like Cat’s Eye.” Ultimately, understanding how it formed provides insight into the eventual fate of our sun, which will one day become a planetary nebula.”
Image: Hubble’s eye in the sky
Ryan Clairmont et al, Morphokinematic modeling of a point symmetric cat eye, NGC 6543: a ring-like remnant of a prior jet, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac2375
Presented by the Royal Astronomical Society
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