In an unprecedented development, astronomers have managed to capture detailed images of a star outside our solar system, including the gas bubbling on its surface.
These images, revealing giant bubbles of hot gas larger than our sun, were obtained from the star R Doradus.
Interestingly, the gas bubbles disappear into the interior of the star faster than expected.
The bubbling surface of R Doradus
“This is the first time that the bubbling surface of a real star can be imaged in this way,” noted study lead author Wouter Vlemmings, a professor at Chalmers University of Technology, Sweden.
“We never expected the data to be of such high quality that we could see so much detail of the convection on the surface of the star.”
How stars create energy is a fascinating process. In their cores, stars undergo nuclear fusion. This amazing energy then rises towards the surface in the form of large bubbles of hot gas – reminiscent of the movement in a lava lamp.
The bubbles eventually cool and descend back into the core in a process known as convection.
The mixing motion of convection helps distribute heavy elements like carbon and nitrogen through the star.
It is also believed to generate stellar winds that propel these elements into the cosmos, contributing to the birth of new stars and planets.
Convection outside our star system
First, a detailed observation of convection motions has been achieved for stars other than our Sun, using the Atacama Large Millimeter/submillimeter Array (ALMA), jointly owned by the European Southern Observatory (ESO).
The target, R Doradus, a red giant star nearly 350 times the diameter of our Sun, is conveniently located about 180 light-years away in the constellation Dorado.
Due to its enormous size and relative proximity to Earth, R Doradus proved to be an ideal candidate for detailed observations. Interestingly, the star has a mass similar to the sun.
The researchers noted that convective bubbles have previously been observed in detail on the surface of stars, including by the PIONIER instrument on ESO’s Very Large Telescope Interferometer.
However, the new ALMA observations track the movement of the bubbles in a way that was not possible before.
Close observations of granular structures
“Convection creates the beautiful grainy structure that we see on the surface of our Sun, but is hard to see on other stars,” explained study co-author Theo Khouri, a researcher at Chalmers.
“With ALMA, we could now not only directly see convective granules – 75 times the size of our sun! – but also measure how fast they move the first time.”
R Doradus granules seem to work on a monthly cycle. This is a faster rate than expected based on the sun’s convection process.
“We do not yet know what is the reason for this difference. “Convection appears to change as the star ages in ways we don’t yet understand,” explained Vlemmings.
Evolution of R Doradus and Sun-like stars
The recent observations are crucial because they deepen our understanding of sun-like stars as they mature into red giants as cool, large and sparkling as R Doradus.
“It’s amazing that we can now directly image details on the surface of stars so far away and observe physics that until now has mostly only been observable in our sun,” said Behzad Bojnodi Arbab, a PhD student at Chalmers who also participated in the study.
Take a look at the future of the sun
The red giant R Doradus offers a preview of what our sun may become in about five billion years. As stars like the sun age, they expand dramatically, becoming cooler and more luminous than red giants.
During this phase, convection becomes the dominant process on their surface, where hot gas rises and cools, forming huge granules of bubbling plasma.
This phase plays a key role in the distribution of elements across the star and into space, enriching the interstellar medium.
Understanding how red giants like R Doradus evolve not only helps astronomers study distant stars, but also sheds light on the eventual fate of our own solar system.
The study is published in the journal Nature.
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