February 14, 2020

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Betelgeuse: A star goes dark

WHow is Orion's shoulder doing? Star fans are always asking themselves this question as soon as they look into the winter night sky. Because the star Betelgeuse, the second brightest star in the constellation of the sky hunter marks his right shoulder, has lost more and more luminosity since the end of last year. The change since then has been drastic: the Red Supergiant, which is more than 700 light years away, now only has 36 percent of its original brightness.

Sibylle Anderl

The decrease in brightness also receives so much attention because one possible reason could be that the star is about to explode as a supernova – an event that we would see so brightly in the night sky that it would cast shadows like the moon. However, two other explanations appear more likely than this spectacular interpretation, which are now supported by new observations with the Very Large Telescope of the European Southern Observatory Eso.

Scientists around astronomer Miguel Montargès from the Belgian KU Leuven observed Betelgeuse at its original luminosity in January last year and have now been able to compare this picture with other observations they have made since December 2019. It becomes clear that not only the brightness but also the apparent shape of the star has changed. This could either be due to the fact that its surface has cooled down in the course of an unusual activity.

Clouds of dust around Betelgeuse in December 2019, recorded at infrared wavelengths by the VISIR instrument on Eso's Very Large Telescope. The star itself is masked.


Alternatively, the star could have emitted larger amounts of dust, which is now in the line of sight between Betelgeuse and us. The evolutionary stage of Betelgeuse is at least known for the fact that there is a strong emission of dust in the vicinity of the star. When astronomers want to observe dust directly, they often use infrared radiation, which the dust emits as thermal radiation. An observation at these wavelengths, made by a French group led by Pierre Kervella from the Paris Observatory, shows the clouds of dust that surround Betelgeuse. Whatever explanation for the loss of brightness is true, the regular look at the unusual development of Betelgeuse remains exciting not only for amateur astronomers. "Of course, our knowledge of the red supergiants is still incomplete, and this is still the subject of intensive research, so that there may still be surprises," said Miguel Montargès.

. (tagsToTranslate) Miguel Montargès (t) Betelgeuse (t) brightness