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Graphics Department MPIA
Artwork: Betelgeuse is a red supergiant star, nearly 1,000 times larger than the Sun.
Astronomers say large cold patches on a “supergiant” star near Earth were behind its surprise attenuation last year.
Red giant stars like Betelgeuse frequently experience changes in brightness, but the drop to 40% of their normal value between October 2019 and April 2020 surprised astronomers.
The researchers now say this was caused by gigantic cold spots similar to the sunspots seen on our own parent star.
It was speculated that Betelgeuse was about to become a supernova.
But the star instead began to recover and by May 2020 it had returned to its original brightness.
Betelgeuse, which is about 500 light years from Earth, is nearing the end of its life. But it is not known precisely when it will explode; it could take up to hundreds of thousands of years or even a million years.
However, when the giant star runs out of fuel, it will first collapse and then bounce off in a spectacular explosion. There is no risk to Earth, but Betelgeuse will light up enormously for a few weeks or months.
It should be visible in daylight and could be as bright as the moon at night.
Because it takes about 500 years for light to reach us, we would be seeing an event that happened centuries ago.
Various scenarios have been presented to explain recent changes in the star’s brightness.
Astronomers have previously considered that the dust produced by the star was obscuring it, causing a sharp decrease in brightness.
Red giants exhibit a behavior known as pulsation, caused by changes in the area and temperature of the star’s surface layers. Pulsations can eject the outer layers of the star with relative ease.
The released gas cools down and turns into compounds that astronomers call dust.
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ESO / M. Montargès et al.
Brightness variations on the Betelgeuse surface before and during its darkening. The asymmetries led the authors to conclude that there are large stars.
To test the idea of dust, astronomers used the Atacama Pathfinder Experiment (APEX) in Chile and the James Clerk Maxwell Telescope (JCMT) at Mauna Kea in Hawaii. These telescopes measure electromagnetic radiation in the submillimeter wave spectral range. The wavelength of this radiation is a thousand times greater than that of visible light.
This part of the electromagnetic spectrum is particularly good for observing the distribution of cosmic dust.
“What surprised us was that Betelgeuse became 20% darker even in the sub-millimeter wave range,” said co-author Steve Mairs of the East Asia Observatory in Taiwan, which operates the JCMT.
The result is not compatible with the presence of dust, the researchers say. Instead, astronomers say, temperature variations in the photosphere, the star’s luminous surface, likely caused the brightness to drop.
“The corresponding high-resolution images from Betelgeuse from December 2019 show areas of variable brightness. Together with our result, this is a clear indication of huge star spots that cover between 50% and 70% of the visible surface and have a higher temperature. lower than the brightest photosphere, “said co-author Peter Scicluna of the European Southern Observatory (Eso).
“By comparison, a typical sunspot is the size of Earth. Betelgeuse’s starburst would be a hundred times larger than the Sun. Betelgeuse’s sudden fade does not mean it becomes a supernova. It is a supergiant star that grows like a super-sized star spot. ” said co-author Professor Albert Zijlstra of the University of Manchester, UK.
Compared to our Sun, Betelgeuse is approximately 20 times more massive and approximately 1,000 times larger. If placed at the center of the Solar System, it would almost reach Jupiter’s orbit.
The findings are published in The Astrophysical Journal Letters.
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