Like an enormous lava lamp, the sun roils with hot bubbles that rise from its belly to the surface, then cool and sink back down into its interior.
This process occurs through convection, distributing heavier elements like carbon and nitrogen throughout the sun. It’s also thought to be a driving force behind solar winds — hot, ionized gasses flowing away from the sun — which spread charged particles into space.
Astronomers have now seen and captured pictures of another star bubbling gas on its surface. The star, R Doradus, is a red giant, with a diameter about 350 times larger than the sun’s. This puffy star is about 180 light-years away from Earth in the southern constellation Dorado.
The ability to watch this process unfold on another star could help scientists understand how convection changes over time as a star ages. Though R Doradus is much larger than the sun, its mass is almost the same, meaning the star is perhaps what the sun will look and act like in another 5 billion years, when it also becomes a red giant and is near death.
“This is the first time the bubbling surface of a real star can be shown in such a way,” said Wouter Vlemmings, lead author of the study, in a statement. “We had never expected the data to be of such high quality that we could see so many details of the convection on the stellar surface.”
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The Atacama Large Millimeter/submillimeter Array, or ALMA, captured the images, seen in the video above, in July and August 2023. The humongous observatory is based in Chile, co-owned by the U.S. National Science Foundation, European Southern Observatory, and National Institutes of Natural Sciences of Japan.
Convection bubbles have been previously spotted on other stars, but the new ALMA observations track the motion of the bubbles in a detailed way that was not possible before. The findings are published in the journal Nature. What the images reveal are giant, hot bubbles of gas appearing and then disappearing beneath the surface at a rate much faster than predicted.
Antennas of the Atacama Large Millimeter/submillimeter Array, or ALMA, in the Chilean Andes point at the night sky.
Credit: ESO / C. Malin
On the sun, these bubbles, known as convective granules, are each about the size of France. In the past two years, the new Daniel K. Inouye Solar Telescope in Hawaii has taken extremely detailed images of these bubbles as it studies the origins of “space weather.” The telescope is working in conjunction with the Solar Orbiter, a collaborative mission of the European Space Agency and NASA launched in February 2020, and the Parker Solar Probe, a NASA spacecraft sent up two years earlier.
Despite the sun being 93 million miles from Earth, solar storms can have serious consequences on technology, disrupting power grids and telecommunications systems on Earth when their radiation reaches the planet’s magnetic field and atmosphere.
But if you thought bubbles the size of France were big, on R Doradus, each bubble is a whopping 75 times the size of the sun, the researchers said.
The new paper also marks the first time astronomers have been able to track how fast the convective granules on another star move. On R Doradus, the bubbles appear to move on a one-month cycle, faster than how convection works on the sun. Scientists don’t yet understand why.
“It is spectacular that we can now directly image the details on the surface of stars so far away,” said Behzad Bojnodi Arbab, a doctoral student at Chalmers University of Technology in Sweden, who contributed to the study, “and observe physics that until now was mostly only observable in our Sun.”
