Observations of Betelguese’s surface have shown that the rapidly dimming supergiant is also changing shape.

Astronomers have observed the ever dimming surface of Betelguese with the aid of the ESO’s Very Large Telescope (VLT). The stunning new images they have captured not only reveal the star’s unprecedented dimming but also that the red supergiant in the constellation of Orion is changing shape.

Betelgeuse began to noticeably dim in late 2019, with the red supergiant’s estimated drop in brightness currently at around 36% of its normal output. This is a change so extreme it is noticeable with the naked eye. Astronomers and researchers across the globe are clamouring to learn more about this drop in brightness and what it signifies for the star.

The red supergiant star Betelgeuse, in the constellation of Orion, has been undergoing unprecedented dimming. This stunning image of the star’s surface, taken with the SPHERE instrument on ESO’s Very Large Telescope late last year, is among the first observations to come out of an observing campaign aimed at understanding why the star is becoming fainter. When compared with the image taken in January 2019, it shows how much the star has faded and how its apparent shape has changed. Image credit: ESO/M. Montargès et al.

Enter Miguel Montargès, an astronomer at KU Leuven in Belgium, and his team. They have been observing Betelgeuse with the VLT since December in an attempt to unravel the cause of the changes it is undergoing. One of their observations takes the form of a stunning image of the star’s surface (above), taken with the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE).

Betelgeuse’s irregular surface is made up of giant convective cells that move, shrink and swell. The star also pulsates, like a beating heart, periodically changing in brightness. These periodic changes are nowhere near as extreme as the changes the star has recently undergone, however. These convection and pulsation changes in Betelgeuse are referred to as stellar activity.

This comparison image shows the star Betelgeuse before and after its unprecedented dimming. The observations, taken with the SPHERE instrument on 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 credit: ESO/M. Montargès et al.

In addition to this image, because the team were also observing Betelguese in January 2019, they have been able to provide a side-by-side comparison that demonstrates just how extreme the star’s dimming is. Both the ‘before’ and ‘after’ images were taken in the visible light spectrum. This like for like comparison (above) also seems to clearly show that Betelguese is changing shape.

The stunning difference in Betelguese’s light output and shape can also be seen in this animation created by ESO.