Betelgeuse’s Great Dimming Event in high resolution

The Great Dimming Event (GDE) of Betelgeuse, where the red supergiant star visibly faded in late 2019 and early 2020, puzzled and fascinated the world as it happened. Some thought that the star, which is coming to the end of its life, was about to explode and go supernova. In this glowing Picture of the Week, astronomers have shed new light on how Betelgeuse became darker, confirming that the GDE wasn’t a precursor to a spectacular supernova after all — sorry!

Here we see Betelgeuse as it was in December 2018, February 2020 and December 2020, capturing the famed star before, during, and after the GDE. A team led by Julien Drevon, Florentin Millour and Pierre Cruzalèbes at the Université Côte d’Azur (France) used the MATISSE infrared instrument on ESO’s Very Large Telescope Interferometer (VLTI) to obtain high-resolution images of the star. The top images here show its “surface” or photosphere, whereas the bottom ones trace silicon monoxide, a molecule that can act as a seed to form dust grains.

The keen eye may notice that Betelgeuse’s photosphere got brighter during the so-called dimming event. We now know dust was being produced during the GDE, which made the star appear dimmer to us in visible light, but brighter to MATISSE as dust glows in infrared light. In addition, the changes in the structure of the photosphere and the silicon monoxide are consistent with both the formation of a cold spot on the star’s surface and the ejection of a cloud of dust.

Betelgeuse’s size on the sky is similar to that of a 1 euro coin seen from 100 km away. The VLTI combines the light of several telescopes to create a much larger “virtual” telescope that can discern small structures on Betelgeuse. Thanks to this, we can witness in detail how this massive star ages and evolves.