An international team of astronomers has conducted some impressive observations of the atmosphere of a red giant star. The star is the same mass as our Sun and this analysis could be used to estimate what the Sun might look like in about 5 billion years.
The researchers used ALMA (the Atacama Large Millimeter/submillimeter Array) to study W Hydrae, which is located 320 light-years from us. W Hydrae is classified as an Asymptotic Giant Branch (AGB) star, a cool, bright, old object slowly losing mass due to its stellar winds. The observations are reported in Nature Astronomy.
“For us it’s important to study not just what red giants look like, but how they change and how they seed the galaxy with the elements that are the ingredients of life. Using the antennas of Alma in their highest-resolution configuration we can now make the most detailed observations ever of these cool and exciting stars,” lead author Wouter Vlemmings, from Chalmers University of Technology in Sweden, said in a statement.
Studying W Hydrae has also given the team a glimpse into the potential future of the Sun. Although similar in mass, the AGB star is much, much bigger. It has a diameter twice as wide as Earth's orbit around the Sun, and if it was located at the center of the Solar System, would extend close to the orbit of Mars.
The observations also gave the team a surprise. They saw a bright spot on the surface suggesting that the star is not just passively aging, but remains active, although the exact nature of such activities is not clear at the moment.
“Our measurements of the bright spot suggest there are powerful shock waves in the star’s atmosphere that reach higher temperatures than are predicted by current theoretical models for AGB stars,” added co-author Theo Khouri, also at Chalmers.
Stars manufacture several elements that are crucial for life like carbon, oxygen, and nitrogen. Since these objects are extremely puffy, the material that makes them is only weakly bound by gravity. Stellar winds can propel this material into space where it ends up forming new stars and planets.
“It’s humbling to look at our image of W Hydrae and see its size compared to the orbit of the Earth. We are born from material created in stars like this, so for us it’s exciting to have the challenge of understanding something which so tells us both about our origins and our future,” stated Elvire De Beck, from Chalmers too.