Astronomers claim that large interesting patches on a “supergiant”
Red giant stars like Betelgeuse often undergo changes in brightness, but the drop to 40% of its normal value between October 2019 and April 2020 surprised astronomers.
Researchers now say this was caused by gigantic cool areas similar to the sunspots seen on our parent star.
Betelgeuse was thought to be becoming a supernova.
But the star instead started to recover and in May 2020 it returned to its original brightness.
Betelgeuse, which is about 500 light years from Earth, is reaching the end of its life. But it is not known exactly when it will explode; it could take up to hundreds of thousands of years or even a million years.
When the giant star runs out, however, it will first collapse and then bounce back into 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.
Since it takes about 500 years for the light to reach us, we would see an event that happened centuries ago.
Various scenarios have been proposed to explain the recent changes in the brightness of the star.
Astronomers previously considered that the dust produced by the star was darkening it, causing the sharp drop in brightness.
The red giants show a behavior known as pulsation, caused by changes in the area and temperature of the surface layers of the star. Pulsations can expel the outer layers of the star with relative ease.
The released gas cools and develops into compounds that astronomers call dust.
To test the idea of dust, astronomers used the Atacama Pathfinder Experiment (APEX) in Chile and the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in Hawaii. These telescopes measure electromagnetic radiation in the spectral range of submillimeter waves. 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 has become 20% darker even in the range of submillimetric waves,” said co-author Steve Mairs of the Taiwanese East Asia Observatory, which manages the JCMT.
The result is not compatible with the presence of dust, say the researchers. Instead, astronomers say, temperature changes in the photosphere – the bright surface of the star – most likely caused the brightness to drop.
“The corresponding high resolution images of Betelgeuse from December 2019 show areas of different 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 temperature lower than the brighter photosphere, “said co-author Peter Scicluna of the European Southern Observatory (Eso).
“For comparison, a typical sunspot is the size of the Earth. Betelgeuse’s stellar point would be a hundred times larger than the Sun. Betelgeuse’s sudden fade does not mean that it is becoming supernova. It is a supergiant star that grows a super – starry star “. said co-author Prof Albert Zijlstra of the University of Manchester in the UK.
Compared to our Sun, Betelgeuse is around 20 times more massive and around 1,000 times larger. If positioned in 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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