Astronomers have spotted a strange spiral of gas and dust winding outward from a giant red star named R Sculptoris.

The elderly star, which is about 1,500 light-years from Earth, is in the final stages of its life and is slowly shedding the outer layers of its atmosphere. Intensely high temperatures at the star's core create a powerful stellar wind that drives these layers out, where they usually accumulate into spectacular objects called planetary nebulas over a few million years. Most small- and medium-sized stars, such as our sun, will undertake this process at the end of their days.

Every 20,000 years or so during this stage, the star will undergo a thermal pulse – a 200-year-long thermonuclear convulsion that happens deep in the star’s core. The star will rapidly fuse helium into heavier elements, releasing tons of energy, brightening greatly, and shedding a high-density shell of material.

“Inside the star a lot of new elements are formed, such as oxygen and carbon,” said astronomer Matthias Maercker of the European Southern Observatory, lead author of the new work, which appeared Oct. 10 in Nature. These are the necessary ingredients for life and such a thermal pulsing process in previous generations of stars helped seed our solar system with the stardust that we are made from.

Scientists have observed these detached shells around many stars but have never glimpsed what was inside of them. Using the Atacama Large Millimeter/submillimeter Array (ALMA), a new radio telescope, Maercker and his team were able to see the spiral structure behind R Sculptoris’ shell. The shape of this formation is likely caused by a previously undetected companion star about 0.2 times the mass of our sun orbiting around R Sculptoris and influencing the way it sheds material.

By calculating the amount of gas and dust in each part of the spiral, scientists can learn a great deal about thermal pulse processes and the interior structure of the star.

“We can walk along the spiral toward the star – it’s sort of like a clock that can tell us what happened when,” said Maercker. Observations show that R Sculptoris suffered a thermal pulse about 1,800 years ago that lasted about 200 years.

Other scientists are praising the finding. “It’s really gratifying to see this new view of a process that we’ve known about for some time but never seen in such detail,” said astronomer Mark Morris of UCLA, who was not involved with the work.

Astronomers have modeled the outflow from the late stages of red giant lives but this research allows them to finally match up their theories with data. The new observations of R Sculptoris, for instance, show that more material is blowing out than was expected from simulations. The finding will help scientists create a more detailed picture of stellar evolution and predict what will happen when our own sun finally meets its end.

The research is also a good indication of the type of detailed work that ALMA will do, said Morris. The array currently has only about a third of its intended 66 telescope antennae built, so future observations will have even higher resolution and likely provide many new surprises for astronomers.

Image: ALMA (ESO/NAOJ/NRAO)