Stars throw out waste carbon in just 1000 years

When cosmic carbon leaves home, it may move in a real rush, according to the first sighting of a star spewing it into space.Ageing stars build elements like carbon in their core. These are eventually shed when stars throw off their surface layers. It's a crucial process for seeding the universe with carbon and oxygen, which are important for life. "All of organic chemistry and life depends on these elements," says Albert Zijlstra of the Jodrell Bank Centre for Astrophysics in Manchester, UK. But no one knew exactly how the elements move outwards from the core. One theory was that the temperature cycles in dying stars could help stir their inner and outer layers, dredging up elements from the core. To test this theory, Zijlstra and his colleagues used the airborne SOFIA telescope to look at a gas cloud around an older sunlike star called BD+30 3639.

They found that the outer part of the cloud, made of gas that left the star long ago, is mostly oxygen. The inner cloud, which left the star recently, is full of carbon. By modelling how the gap between the layers evolved, they were able to work out that the star took 1000 years to dredge up its carbon. "Even though 1000 years sounds like a lot, for a star it really means a very short time," says Lizette Guzman-Ramirez of the European Southern Observatory in Santiago, Chile. "What we witnessed is the equivalent of a 40-minute event in the life of a human being."

"The unique result of this paper is really that one is witnessing the transition from an oxygen to a carbon-rich object," says Leen Decin of the Catholic University of Leuven (KUL) in Belgium, who was not involved in the study. "It is almost [like] finding a needle in a haystack."