(ORDO NEWS) — A team of scientists and a high school graduate have reconstructed the complex and mysterious clumps of dust and gas that make up one of the most famous stellar “ghosts” in the sky, the Cat’s Eye Nebula.
The new model has revealed mechanisms that have shaped some of the previously unexplained aspects of the nebula’s structure.
The Cat’s Eye Nebula, also known as NGC 6543, is a planetary nebula. However, it is not associated with the planets at all; the term arose only because their round shape resembles the planets visually.
Such nebulae are what remains after a star has run out of fuel to burn and has reached the end of its life.
While planetary nebulae share common characteristics, the Cat’s Eye Nebula is one of the most complex examples discovered to date.
In general, it has a round shape, but its inner part is dominated by a diamond-shaped structure, similar to the pupil of a cat’s eye, filled with knots, shells and filaments.
How nebulae are born
It is also one of the most studied nebulae in the sky, but some aspects of its structure are still puzzling.
They are not easily explained within the current model of planetary nebula formation, called the interacting stellar wind model.
According to this model, the star expands into a red giant (like Betelgeuse) and creates a slow stellar wind that pushes stellar material into space.
Then, at the end of this life stage, the star ejects its outer material into space, and the core, no longer supported by the external pressure of nuclear fusion, collapses under gravity to form a white dwarf.
A very hot white dwarf generates a fast stellar wind that slams into material in slower winds, shaking the gas and creating shells.
However, the almost perfectly symmetrical bipolar shape of the Cat’s Eye Nebula does not fit this model.
Ryan Claremont, who plans to attend Stanford University, enlisted the help of astronomers Wolfgang Steffen of the National Autonomous University of Mexico and Niko Koning of the University of Calgary in Canada and used the SHAPE astrophysical modeling software to deconstruct what is happening inside the central region of the Cat’s Eye Nebula.
The 3D model they built revealed something interesting: spiraling rings of high-density gas, partially wrapped around the nebula’s outer shell, arranged symmetrically around its two lobes.
This symmetry suggests that the rings are the result of high-velocity jets ejected from the star’s poles at the center of the Cat’s Eye.
As the star that gave birth to them wobbled like a top – a motion called rotational precession – this caused the jets to emerge in a spiral shape.
Their incompleteness means that the jets erupted for only a short time before being interrupted.
The only object known to produce a precessing jet in a planetary nebula is a binary star. The star at the center of the Cat’s Eye is thought to be a Wolf-Rayet type star, not quite a white dwarf yet, but just around the corner, still losing mass as the last of its fuel is burned.
Such stars combined with another star can create truly impressive nebulae.
Previous research has suggested that a double companion may be lurking at the heart of the Cat’s Eye Nebula.
This new discovery supports this interpretation. Future observations and analysis will be able to take this model into account to better interpret the strange dynamics of this enchanting ghost of a dying star.
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