Spiral found round dying star

Posted by Kate Taylor

A completely unexpected spiral structure observed around an ancient star could offer a glimpse of what our own sun has in store.

Astronomers using the Atacama Large Millimeter/ submillimeter Array (ALMA) discovered the spiral around the old star R Sculptoris. It's the first time that such a structure, along with an outer spherical shell, has been found around a red giant star.

The strange shape was probably created by a hidden companion star orbiting the red giant.

"We've seen shells around this kind of star before, but this is the first time we've ever seen a spiral of material coming out from a star, together with a surrounding shell," says Matthias Maercker of ESO and the University of Bonn.

Stars with masses up to eight times that of the sun eventuallybecome red giants and lose a large amount of their mass in a dense stellar wind.

During this stage, they also periodically undergo thermal pulses: short-lived phases of explosive helium burning in a shell around the stellar core. This blasts material off the surface of the star at a much higher rate, creating a large shell of dust and gas around the star.

Thermal pulses occur every 10,000 to 50,000 years or so, and last only a few hundred years. The new observations of R Sculptoris show that it went through one about 1,800 years ago, lasting for about 200 years. The companion star shaped the wind from R Sculptoris into a spiral structure.

"In the near future, observations of stars like R Sculptoris with ALMA will help us to understand how the elements we are made up of reached places like Earth," says Maercker. "They also give us a hint of what our own star's far future might be like."