Betelgeuse star dimming mystery accidentally solved by weather satellite


Betelgeuse’s sudden dimming in 2019 has baffled astronomers ever since, but we’ve now pinpointed the cause


May 30, 2022

Artist’s impression of Himawari-8 and Himawari-9


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

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

Previous research had suggested that a cloud of dust and a cool spot on the star could be 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 Earth’s weather.

The satellite- Himawari-8 – is used to continuously observe the weather in Japan and surrounding areas from a geostationary position nearly 36,000 kilometers away. However, he also occasionally sees stars appear beyond the edges of the Earth, including Betelgeuse once a day.

Taniguchi used publicly available data from the satellite to collect 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 temperature of the star also dropped 140°C.

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

The cause of the sudden dust generation is unclear. It may be a shock wave in the star that expelled gas outward which then condensed into dust. This could also explain the star’s subsequent cooling, although it is not yet certain whether the events are related.

Taniguchi has already planned to use Himawari-8 to observe more stars, to examine their evolution and dust production, and other weather satellites could be just as useful to astronomers. “I hope that after this article is published, other satellites will open their data publicly,” he says.

Journal reference: natural astronomy, DOI: 10.1038/s41550-022-01680-5

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