Artistic impression of what our Earth may look like 5-7 billion years from now, when our red giant Sun swells.
Credit: Wikimedia
PARIS: New observations from NASA's Kepler spacecraft have allowed astronomers to distinguish between two different types of red giant star – those that burn hydrogen in their cores and those that also burn helium - and could shed light on the fate of our Sun.
The Sun will itself become a red giant about five billion years from now, and when this transformation happens, it will engulf some of the inner plants of the Solar System and make life on Earth impossible. While stellar evolution theory had already predicted the presence varying oscillation patterns that cause the differentiation in red giants, these new observations are the first to confirm it.
“They allow us tell red giants apart and we will now be able to compare stars that are different stages of their evolution in a way that we couldn't before,” said lead author Tim Bedding of the University of Sydney.
Things look similar on the surface
For most of their lives, stars shine thanks to the energy released by nuclear reactions in their cores that transform hydrogen into helium.
With time, however, the hydrogen in the core eventually runs out and stars then begin burning the hydrogen in a shell around the core, and finally the helium in their cores.
On the surface, hydrogen- and helium-burning stars look very much the same same (both have bloated to many hundreds of times their original size), belying the profound changes that are taking place deep within them.
Following the ‘starquakes’
The changes in brightness at a star's surface are a result of turbulent motion inside it. This natural motion, which occurs in our own Sun too, causes perpetual ‘starquakes’, creating sound waves that travel down through the interior of the star and then back up to the surface.
Under the right conditions, these waves interact with other waves trapped inside the star's core.
“It is these 'mixed' oscillations that are key to understanding a star's particular life stage - that is, whether it is burning hydrogen or helium,” said Bedding, whose team published their observations in the journal Nature.
