Why the star of Orion’s left shoulder is fading

Betelgeuse is a red supergiant. With a diameter 1000 times that of the Sun’s and – formerly – 10,000 times the illuminance, it has wowed the entire Milky Way, but now it’s even being mentioned on the cable news shows. Why? Because everyone’s hoping for a catastrophe. If such a large star fades to 36 percent of its previous illuminance within a short time, it would suggest it might soon end in a supernova. That would certainly be spectacular, because it would grace the Earth’s night skies with the brightness of a half moon.

But the hope that this fireworks display will go off sometime in our lifetime is probably still too premature. Astronomers of the European Southern Observatory have shown with the help of the Very Large Telescope that Betelgeuse really has changed in apparent shape and brightness (see the images below). But that could also be due to a giant dust cloud ejected by the star, which is more than 700 light-years away, obscuring our view. It could also be possible that the surface has cooled significantly due to some unusual stellar activity.

This comparison shows the star Betelgeuse before and after its unprecedented darkening. These observations, which were made with the SPHERE instrument on the ESO’s Very Large Telescope in January and December 2019, show how much the star has faded and how its apparent shape has changed. (image: ESO/M. Montargès et al.)
This image, which was made with the VISIR instrument on the ESO’s Very Large Telescope, shows infrared light captured in December 2019 from the dust in the region around Betelgeuse. The dust clouds, which resemble flames in this spectacular image, were produced when the star flung its matter back into space. The black disk masks the center of the star and a large part of its surroundings. These are very bright and must be masked to be able to see the fainter dust clouds. The orange-colored spot in the center is the SPHERE image of the surface of Betelgeuse, which has a size similar to that of Jupiter’s orbit. (image: ESO/P. Kervella/M. Montargès et al., Acknowledgement: Eric Pantin)
This illustration shows the supergiant, Betelgeuse, made visible thanks to various high-tech methods using the ESO’s Very Large Telescope. Two independent teams of astronomers were able to produce the sharpest views of the supergiant, Betelgeuse, to date. They show that the star has giant gas plumes that are almost as large as our Solar System. Another gigantic bubble is getting ready to burst on its surface. These discoveries provide important clues to how these giants cast off matter at enormous velocities. A scale in units of Betelgeuse radii and a comparison with the Solar System are also shown. (image: ESO/L. Calçada)

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