Betelgeuse's wild surface appears puzzling to our telescopes: ScienceAlert

There's something strange about the dying star Betelgeuse.

Yes, there was the whole sneezing thing. This has been largely resolved for now. But before the great dimming catastrophe of 2019, scientists discovered something even stranger about the giant star. Radio measurements of its changing light indicate that it was rapidly rotating 5 kilometers (3.1 miles) per second.

The big problem with this is that Betelgeuse-type stars, in theory, should have a maximum rotation speed at least two times lower. So, astronomers wonder, what does this give?

Well, according to new research, these may have been ancient and deceptive doodles. A team led by astrophysicist Jing-Ze Ma of the Max Planck Institute for Astrophysics in Germany found that Betelgeuse's boiling surface can be so riotous that it generates the illusion of rapid rotation.

Rotation in stars is measured by carefully analyzing differences in light from opposite sides of the star. Light from the side of the star moving toward the view (that's us) gets a little push that squishes it toward the blue end of the spectrum, while light from the side moving away from us stretches toward the red end.

Scientists can measure the amplitude of this blue-red shift to determine how fast the star is rotating. Well, a typical quiet star, anyway. The problem is that Betelgeuse is not quiet. It is in the red super giant stage of its life; It ran out of nuclear fuel and swelled to enormous size, with convective boiling of the surface.

Bubbles rise from hot materials, cool, and then fall to the bottom. This happens in the Sun too, with convection cells the size of Texas, but the process is even more violent at Betelgeuse, where convection cells can be as large as the Earth's orbit around the Sun (Gemini's armpit is large enough to It extends to the orbit of Jupiter).

Ma and his colleagues wanted to know whether this convection could provide an alternative explanation for what we had previously interpreted as ultrafast rotation in observations from the Atacama Large Millimeter/submillimeter Array (ALMA), so they turned to 3D simulations.

They created models of red giant stars like Betelgeuse, governed by giant convection it's not Alternately, the results are then processed as ALMA composite observations.

Their simulations showed that massive convection cells rise on one side of the red giant, while another group collapses and falls inward on the other side. ALMA does not have the ability to identify these cells as convection cells; Instead, the data from the telescope can look very similar to rotation.

In fact, the researchers showed that in 90% of simulations, observations made with ALMA would appear to rotate at a rate of several kilometers per second.

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This is not strong evidence that Betelgeuse is not rotating very fast, although it does show that we cannot reach a conclusion based on the data we currently have. But more high-resolution observations have been made, and are being processed and analyzed. These should give us more clues about what the star is doing.

Either way, the results will be interesting. If Betelgeuse is spinning like a confused vortex, it could mean that the massive red giant gained spin by gobbling up a smaller companion star. If it had rotated more quietly, we might have learned to proceed with more caution when interpreting the data we collect on unstable stars.

“There is a lot we still don't understand about giant boiling stars like Betelgeuse.” says astronomer Andrea Chiavasa The French National Center for Scientific Research.

“How does it really work? How does it lose mass? What particles can form in its outflows? Why is Betelgeuse suddenly less bright? We're working hard to make our computer simulations better and better, but we really need the amazing data from telescopes like ALMA “

The team's research has been published in Astrophysical Journal Letters.