The nebula, formally known as NGC 6543, is as enigmatic as the phantom character from J.R.R. Tolkien. Though the Cat’s Eye Nebula was one of the first planetary nebulae discovered, it is also one of the most complex. When Sun-like stars gently eject their outer gaseous layers, they form bright nebulae with amazing and perplexing shapes.
One of the most complex and least understood nebulae, a whirling landscape of gas and dust left in the wake of a star’s death throes, is about 3,000 light-years from Earth. A new computer visualization reveals the 3-D structure of the Cat’s Eye nebula and hints at how it was sculpted by not one, but two dying stars.
Based on Hubble Space Telescope images, the digital reconstruction reveals two symmetric rings around the nebula’s edges. Ryan Clairmont and colleagues report in the October Monthly Notices of the Royal Astronomical Society that the rings were most likely formed by a spinning jet of charged gas launched from two stars in the nebula’s center.
Based on Hubble Space Telescope images, the digital reconstruction reveals two symmetric rings around the nebula’s edges. Ryan Clairmont and colleagues report in the October Monthly Notices of the Royal Astronomical Society that the rings were most likely formed by a spinning jet of charged gas launched from two stars in the nebula’s center.
“I realized there hasn’t been a comprehensive study of the structure of the nebula since the early ’90s,” says Clairmont, an undergraduate at Stanford University. Last year, while a high school student in San Diego, he reached out to a couple of astrophysicists at a scientific imaging company called Ilumbra who had written software to reconstruct the 3-D structure of astronomical objects.
The team combined Hubble images with ground-based observations of light at various wavelengths to reveal the nebula’s gas motions. Identifying which parts were moving toward and away from Earth aided in revealing its three-dimensional structure.
The researchers discovered two partial rings on either side of the nebula’s center. The rings’ symmetry and unfinished nature indicate that they are the remains of a plasma jet launched from the nebula’s heart and suffocated before it could complete a full circle. According to Ilumbra partner Wolfgang Steffen, who is based in Kaiserslautern, Germany, such jets are usually formed by an interaction between two stars orbiting each other.
Clairmont’s work was recognized at the 2021 International Science and Engineering Fair, an annual competition sponsored by the Society for Science, which publishes Science News. Steffen was skeptical of the short deadline — when Clairmont contacted him, he had only two months to finish the project.
“I said it was impossible!” “No one has tried that before, not even Ph.D. students,” Steffen says. “He did an excellent job. He accomplished everything we had hoped for and more.”
Astronomers were surprised to see bull’s-eye patterns around planetary nebulae 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 magnetic activity cycles similar to our Sun’s sunspot cycle, the action of companion stars orbiting the dying star, and stellar pulsations. Another school of thought holds that the material is ejected smoothly from the star, and the rings form later as a result of the formation of waves in the outflowing material. More observations and theoretical studies will be required to distinguish between these and other possible explanations.
Around 1,000 years ago, the pattern of mass loss abruptly changed, and the Cat’s Eye Nebula began to form within the dusty shells. It has been growing ever since, as evidenced by Hubble images taken in 1994, 1997, 2000, and 2002. The question is, what caused this dramatic shift? Many aspects of the process that causes a star to lose its gaseous envelope are still unknown, and studying planetary nebulae is one of the few ways to learn about the last few thousand years of a Sun-like star’s life.
