Astronomers now have their most detailed view yet of the Helix nebula, one of the closest planetary nebulae to Earth.
The image comes from the VISTA telescope, the world's largest survey telescope, at the Paranal Observatory in Chile. Using infrared light filters, scientists have colored the image to reflect the spectrum of radiation from the nebula. It's the best image yet of the Helix nebula, said Jeremy Walsh, a scientist at the European Southern Observatory in Germany.
Contrary to its name, a planetary nebula does not include a planet. Rather, it forms like this: As a star ages and gets larger, the gas that surrounds it starts to get blown off into a large, fuzzy ball of gas. The star heats up and lights up the nebula, which refers to the molecular gas, ionized metal and dust around it.
The Helix nebula resides in the constellation Aquarius about 700 light-years away. It's quite large - its main ring is 2 light-years across, although its material spreads out to 4 light-years. The star at its center is evolving to become a white dwarf.
This image shows the nebula in the infrared light spectrum, which is invisible to the eye and more toward heat radiation. Telescopes that capture only visible light have not been able to get such a detailed view of the nebula.
"It’s a great target for the VISTA telescope because it has a big field, it can cover a large part of the area of the sky," Walsh said.
The gas in the nebula is mainly hydrogen, with about 10% helium and 1% other elements, Walsh said.
Unlike in visible-light images of the Helix nebula, this one reveals its cometary knots, which are strands of hydrogen that can be as big as our solar system. These clumps of gas and dust endure despite the high-energy radiation coming from the dying star. Their shape is a little bit like a comet, but they're not comets. One of the mysteries is how these cometary knots originated.
"Were they thrown out by the star as it expanded, or have they formed in the cloud of gas somehow through some instability, like forming clouds in the sky? Perhaps it's an equivalent sort of process," Walsh said. "It still is an active area of research."