Researchers have created the first three-dimensional computer-generated model of the Cat’s Eye Nebula, revealing a pair of symmetrical rings circling the nebula’s outer shell. The symmetry of the rings suggests they were formed by a precessional jet, providing strong evidence for a binary star at the center of the nebula. The study was led by Ryan Clairmont, who recently graduated from high school in the United States, and is published in Royal Astronomical Society Monthly Notices.
A planetary nebula forms when a dying solar-mass star ejects its outer layer of gas, creating a colorful shell-like structure characteristic of such objects. The Cat’s Eye Nebula, also known as NGC 6543, is one of the most complex planetary nebulae known. It lies just over 3,000 light years from Earth and can be seen in the constellation of Draco. The Cat’s Eye Nebula was also imaged by the Hubble Space Telescope in high resolution, revealing a complex structure of knots, spherical shells and arc-shaped filaments.
The nebula’s mysterious structure has baffled astrophysicists because it could not be explained by previously accepted theories for the formation of planetary nebulae. More recent research has shown precession jets to be potential shaping mechanisms in complex planetary nebulae such as NGC 6543, but a detailed model has been missing.
Ryan Clairmont, an astronomy enthusiast, decided to try to establish the detailed 3D structure of Cat’s Eye to learn more about the potential mechanism that gave it its complex shape. To do this, he enlisted the help of Dr. Wolfgang Steffen of the National Autonomous University of Mexico and Nico Koning of the University of Calgary, who developed SHAPE, a 3D astrophysical modeling software particularly suited to planetary nebulae.
To reconstruct the nebula’s three-dimensional structure, the researchers used spectral data from the San Pedro Martir National Observatory in Mexico. These provide detailed information about the internal movement of matter within the nebula. With this data and images from the Hubble Space Telescope, Clairmont built a new 3D model, establishing that rings of high-density gas were wrapped around the outer shell of the cat’s eye. Amazingly, the rings are almost perfectly symmetrical to each other, suggesting they were formed by a jet – a stream of high-density gas ejected in opposite directions from the nebula’s central star.
The jet showed precession, similar to the oscillating motion of a spinning top. As the jet wavered or preceded it drew a circle, creating the rings around the cat’s eye. However, the data indicates that the rings are only partial, meaning that the precession jet never completed a full 360 degree rotation and that the emergence of the jets was only a phenomenon of short duration. The duration of flows is important information for the theory of planetary nebulae. Given that only binary stars can power a precessional jet in a planetary nebula, the team’s findings are strong evidence that such a system exists at the center of Cat’s Eye.
As the angle and direction of the jet changed over time, it likely formed all of the features seen in cat’s eye, including jets and knots. Using the three-dimensional model, the researchers were able to calculate the inclination and the opening angle of the precession jet depending on the orientation of the rings.
Ryan Clairmont, the paper’s lead author and now an undergraduate student at Stanford University, says: “When I first saw the Cat’s Eye Nebula, I was amazed. by its beautiful, perfectly symmetrical structure. I was even more surprised that its 3D structure was not quite understood.”
He adds: “It was very rewarding to be able to do my own research in astrophysics that really has an impact on the ground. Precessing jets in planetary nebulae are relatively rare, so it is important to understand how they contribute to the formation from more complex shapes to systems like the cat’s eye. Ultimately, understanding how they form provides insight into the eventual fate of our Sun, which will itself one day become a planetary nebula.
Image: Hubble spy eye in the sky
Ryan Clairmont et al, Morphokinematic modeling of the point-symmetry cat’s eye, NGC 6543: Ring-shaped remnants of a precessing jet, Royal Astronomical Society Monthly Notices (2022). DOI: 10.1093/mnras/stac2375
Provided by the Royal Astronomical Society
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