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'Hot Spot' Around Red Giant Star May Reveal Sun's Fate
A wide view, in visible light, of the star W Hydrae and the surrounding sky. W Hydrae is similar in mass to Earth's sun but is nearing the end of its life.
Credit: Digitized Sky Survey

Astronomers have captured a stunning new view of the surface of an aging red giant star, revealing new clues about what the future may hold for our own sun. 

The star, known as W Hydrae, is located 320 light-years away, in the constellation Hydra, the water snake. W Hydrae has the same mass as Earth's sun, but it is nearing the end of its life and has swelled to an enormous size — its diameter is twice the size of Earth's orbit around the sun. 

Using the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope in Chile, astronomers from Chalmers University of Technology in Sweden observed W Hydrae up close. The new images provide the clearest view yet of the surface of a red giant that has the same mass as the sun, according to a statement from the university. [Meet ALMA: Amazing Photos from Giant Radio Telescope]

"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," Wouter Vlemmings, an astronomer at Chalmers University and lead author of the study, said in the statement.

W Hydrae is an extremely bright, cool star categorized as an asymptotic giant branch (AGB) star. As stars of this type age, they grow bigger and cooler. Then, when they reach the red giant stage, they release stellar material into space. Earth's own sun is expected to follow a similar path and eventually turn into a red giant star. 

"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," Vlemmings said. 

This is the sharpest image ever taken of the star W Hydrae, which has the same mass as Earth's sun but has swollen to an enormous size. The dotted line shows the diameter of Earth's orbit around the sun, for comparison.
This is the sharpest image ever taken of the star W Hydrae, which has the same mass as Earth's sun but has swollen to an enormous size. The dotted line shows the diameter of Earth's orbit around the sun, for comparison.
Credit: ALMA (ESO/NAOJ/NRAO)/W. Vlemmings)

Specifically, the recent ALMA images show evidence of unexpected processes taking place at the star's surface. The team discovered "an unexpectedly compact and bright spot" around the star, indicating the presence of a hot gas layer in a region of the star’s atmosphere known as the 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," Theo Khouri, an astronomer at Chalmers and co-author of the study, said in the statement

This image shows the red giant star W Hydrae 320 light-years away with the orbits of the planets in our solar system (Earth's orbit shown in blue) superimposed to show the massive size of the dying star. Our sun will likely suffer the same fate.
This image shows the red giant star W Hydrae 320 light-years away with the orbits of the planets in our solar system (Earth's orbit shown in blue) superimposed to show the massive size of the dying star. Our sun will likely suffer the same fate.
Credit: ALMA (ESO/NAOJ/NRAO)/W. Vlemmings

Another possible explanation for the bright spot could be that a giant flare occurred at the time the observations were made. The astronomers plan to further study W Hydrae to better understand what, exactly, is going on in the star’s atmosphere. This research might also shed light on the fate of our own sun, the researchers said.  

"It's humbling to look at our image of W Hydrae and see its size compared to the orbit of the Earth," Elvire De Beck, an astronomer at Chalmers and co-author of the study, said in the statement. "We are born from material created in stars like this, so for us it's exciting to have the challenge of understanding something which … tells us both about our origins and our future."

Their findings were published Oct. 30 in the journal Nature Astronomy. 

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