Astronomers capture detailed image of red giant star

Observations shed light on the ultimate fate of our Sun.
By Laurel Kornfeld | Nov 11, 2017
A research team led by astronomers at Sweden's Chalmers University of Technology has captured the most detailed yet image of a red giant star, providing insight into the fate of the Sun several billion years from now.

The scientists observed W. Hydrae, a red giant located in the constellation Hydra approximately 320 light years away, using the Atacama Large Millimeter/Submillimeter Array (ALMA) telescope in Chile.

Initially a star with approximately the same mass as the Sun, W. Hydrae is now an asymptotic giant branch (AGB) star, meaning it has left the main sequence on the Hertzsprung-Russell diagram, which classifies stars by their luminosity and temperature.

Stars leave the main sequence once they have consumed all the hydrogen in their cores.

At the AGB stage, red giant stars become cool, puff up, and start experiencing rapid mass loss due to stellar winds. Elements manufactured in their cores during their main sequence lives, such as nitrogen and carbon, are expelled into space during this stage.

Eventually, these elements build a new generation of stars as well as seed the galaxy with the materials necessary for life.

ALMA images show W. Hydrae to have swollen to twice the diameter of Earth's orbit around the Sun with an atmosphere subject to massive shock waves.

One particular feature on the star, a compact bright spot, caught the scientists by surprise. They attribute the spot to an unexpected layer of hot gas located above the star's surface, known as its 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 Chalmers astronomer and study team member Theo Khouri.

An alternate explanation for the spot is that the star was experiencing a giant flare when it was observed.

To better understand W. Hydrae's unusual atmosphere, the scientists are conducting followup observations of it using both ALMA and other instruments.

"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 for life," emphasized research team leader Wouter Vlemmings.

"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."

Findings of the study have been published in the October 30 issue of the journal Nature Astronomy.



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