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The loss of brightness of Betelgeuse as seen by the Matisse instrument at the VLTI

2 November 2023

Obtained by scientists at the Observatoire de la Côte d’Azur, using the Matisse instrument at ESO’s VLTI, new images of Betelgeuse appear in a Letter in the journal Monthly Notices of the Royal Astronomical Society, on October 23, 2023. They provide a closer look at the loss of brightness suffered by the massive star in late 2019, and deciphered in 2021 by a researcher from Observatoire de Paris - PSL.

The Great Darkening of Betelgeuse, an episode during which the red supergiant star evidently lost its brilliance between late 2019 and early 2020, left the scientific community in a state of surprise and uncertainty.

Some had assumed that the star, at the end of its life, was about to explode, before transforming into a supernova. Not so, according to a study established in 2021, led by Miguel Montargès, researcher at Observatoire de Paris - PSL.

More recently, using the MATISSE infrared instrument on ESO’s Very Large Telescope Interferometer (VLTI), a scientific team led by astronomers from the Université Côte d’Azur and including Miguel Montargès, took a new, high-resolution look at the star. Here, Betelgeuse’s size on the sky is similar to that of a 1 euro coin, seen from a distance of 100 km.

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Read also
◾ on the ESO website:
Image of the Week: "Betelgeuse’s Great Dimming Event in high resolution"
◾ on the OCA website [in French] :
News from the Lagrange laboratory: "We are all stardust... "

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The VLTI combines the light from several telescopes to create a much larger "virtual" telescope, capable of discerning small structures on Betelgeuse. As a result, this massive star can be examined in detail as it ages and evolves.

Image of the week on the ESO website :
The mid-infrared images captured by the MATISSE instrument are sensitive to the dust produced by the star in its end-of-life phase, while this same dust obscures visible light. The MATISSE images show a luminous overintensity, at the very moment of the star’s famous fading in late 2019 - early 2020.

Bételgeuse
Bételgeuse
The top images show its "surface" or photosphere. The lower images trace silicon monoxide, a molecule that can act like a seed, to form dust grains.
© ESO/J. Drevon et al.


The molecules detected correspond to the precursors of dust formation and the fundamental building blocks of life, making it possible to :

  • show how dust forms around the star
  • highlight a major change in the star’s atmosphere between the two periods.

The attentive observer will notice that at the wavelengths (or colors) at which MATISSE observes, Betelgeuse’s photosphere became brighter during the so-called darkening period.

We now know that dust was produced during the strong flare at the end of 2019, making the star appear darker in visible light, but... brighter for MATISSE, as dust shines in infrared light. Moreover, changes in the photospheric structure and in the silicon monoxide layer are consistent with the formation of a cold spot on the star’s surface and the ejection of a dust cloud.

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