Astronomers have imaged surface changes caused by constant heating inside a star 180 light-years away.
The three snapshots show the changing patterns over a two-week period of R Doradus, a red giant star about 350 times the diameter of the Sun that is churning and boiling with convection currents as it nears the end of its life.
The new study marks the first time humans have been able to image this process on a star other than the one at the center of our solar system. The changes astronomers traced on the surface of R Doradus show giant bubbles of heated gas – 75 times the size of our sun – rising to the surface and then sinking back down, on timescales much shorter than astronomers had expected.
“This is the first time we’ve been able to show the bubbling surface of an actual star like this.” Astronomer Wouter Flemings says: “We did not expect the quality of the data to be high enough to allow us to observe convection on the stellar surface in such detail,” said researchers from Chalmers University of Technology in Sweden.
If we want to understand the surface-level variations of stars other than the Sun, R Doradus is a great object to study. It’s very large, meaning it has a large surface area and a lot of stellar activity. Its larger size and greater activity make it easier to image in order to see significant detail even at this relatively short interstellar distance.
Stars have a process of convection, where heat generated in the core bubbles up to the surface. In the Sun, convection particles tend to be found around the periphery. 1,000 kilometers It has a diameter of 620 miles, a little smaller than the state of Texas, and rises from the center and fades out the edges, lasting for about 20 minutes before disappearing.
At greater depths, granulation occurs on a larger scale. Meso Granules The grains are about 5,000 to 10,000 kilometers in diameter and have a lifespan of about three hours. Super Granules It has a diameter of about 32,000 kilometers and stays in the air for about 20 hours.
Vlemmings and his colleagues used the powerful Atacama Large Millimeter/submillimeter Telescope in Chile to try to tease out the details of this process in another star far away from our solar system, and the results were surprising.
“Convection creates the beautiful granular structure we see on the surface of the Sun, but it’s hard to see on other stars.” Astronomer Theo Khoury says: Chalmers University of Technology.
“ALMA not only allows us to directly observe convective particles 75 times larger than the Sun, but also, for the first time, to measure their travel speeds.”
The convective particles are huge, but researchers don’t fully understand why: R Doradus’ particles could be the equivalent of red giant mesoparticles or superparticles, or they could be different kinds of particles that are unique to red giants, or different types of particles could overlap and produce noticeable effects.
At this time, we cannot directly link the R Doradus particles to the known motion of the Sun. We know that the particles are related to convection, but we don’t currently know what makes them so massive.
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Furthermore, the granules seen in R Doradus seem to have a periodicity of about one month, which is much faster than expected given those observed on the Sun.
But red giants are very different from our Sun in the middle of its life. Red giants get their energy from shell burning, which uses up hydrogen in their cores and fuses it in a shell around their core. This process causes the star to swell to many times its original size. Astronomers predict that during the Sun’s red giant phase, it could expand to the orbit of our Sun. Mars.
There’s a lot we don’t know about red giants because of the limitations of what we can see from this far away, and the very short lifetimes of the convecting particles compared to solar particles may be normal at this stage in the star’s life.
“The reason for this difference is not yet known. It seems that convection changes as the star ages, but we don’t yet know why.” Vlemmings says:.
R Doradus images represent a first, very important step towards understanding these unusual changes.
This study Nature.
