Images captured by the ALMA telescope show that the star is a giant, its diameter twice the size of Earth's orbit around the Sun, but also that the star's atmosphere is affected by powerful, unexpected shock waves, researchers said.
A team led by Wouter Vlemmings from Chalmers University of Technology in Sweden created sharpest observations yet of the star with the same starting mass as the Sun.
The new images show for the first time details on the surface of the red giant W Hydrae, 320 light years distant in the constellation of Hydra, the Water Snake.
W Hydrae is an example of an AGB (asymptotic giant branch) star. Such stars are cool, bright, old and lose mass via stellar winds, researchers said.
Stars like the Sun evolve over timescales of many billion years. When they reach old age, they puff up and become bigger, cooler and more prone to lose mass in the form of stellar winds, they said.
Stars manufacture important elements like carbon and nitrogen. When they reach the red giant stage, these elements are released into space, ready to be used in subsequent generations of new stars.
ALMA's images provide the clearest view yet of the surface of a red giant with a similar mass to the Sun.
Earlier sharp images have shown details on much more massive, red supergiant stars like Betelgeuse and Antares.
The presence of an unexpectedly compact and bright spot provides evidence that the star has surprisingly hot gas in a layer above the star's surface: a chromosphere.
"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," said Theo Khouri, astronomer at Chalmers and member of the team.
An alternative possibility is at least as surprising: that the star was undergoing a giant flare when the observations were made, researchers said.
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