Betelgeuse star dimming mystery accidently solved by weather satellite

The sudden dimming of Betelgeuse in 2019 has been puzzling astronomers ever since, but now we have nailed down the cause

By Jonathan O’Callaghan

A weather satellite making routine observations of Earth may have solved the mystery of why the star Betelgeuse briefly lost its shine.

In late 2019, the red supergiant star, which is about 550 light years from Earth, suddenly became a lot fainter, an event known as the Great Dimming.

Previous research had suggested a cloud of dust and a cool spot on the star may have been the cause. Daisuke Taniguchi at the University of Tokyo, Japan, now believes we know for sure thanks to an unlikely source: a satellite designed to monitor weather on Earth.

The satellite – Himawari-8 – is used to continuously observe weather in Japan and nearby regions from a geostationary position nearly 36,000 kilometres up. It also occasionally sees stars appear beyond the edges of Earth, however – including Betelgeuse once per day.

Taniguchi used publicly available data from the satellite to gather regular infrared observations of the star. These, he says, allowed him to confirm the cause of the Great Dimming, which lasted until early 2020. There was indeed a cloud of dust, picked up by the satellite’s instruments, and the star’s temperature also dropped by 140°C.

“The advantage of Himawari-8 over other telescopes is it is a monitoring telescope,” says Taniguchi. “We saw Betelgeuse every day for five years [from 2017 to 2021].”

The cause of the sudden dust production isn’t clear. It may have been a shockwave in the star that expelled gas outwards that then condensed into dust. This could also explain the subsequent cooling of the star, although it isn’t yet certain if the events were related.

Taniguchi already has plans to use Himawari-8 to observe more stars, to examine their evolution and dust production, and other weather satellites could be similarly useful to astronomers. “I hope after the publication of this paper, other satellites will publicly open their data,” he says.

Journal reference: Nature Astronomy, DOI: 10.1038/s41550-022-01680-5

Sign up to Lost in Space-Time, a free monthly newsletter on the weirdness of reality