Astronomers unexpectedly capture the ‘great dimming’ of supergiant star Betelgeuse

Just months before the COVID-19 pandemic began in early 2020, the world was obsessed with a distant supergiant star, 700 light-years away known as Betelgeuse. The Monstrous Furnace suddenly darkened, becoming 10 times darker than usual. Some suggested it heralded an explosion, but rumors of the star’s disappearance were greatly exaggerated. It cleared up a few months later.

Several teams set out to try to explain what caused this “Great Dimming” with one team analyzing hundreds of images of the star to reveal that stardust was likely obscuring our view from Earth. In June 2021, they showed that Betelgeuse had probably spewed gas, which then cooled, condensed and darkened the star. Another group suggested that the star was also cooling a bit, and that this variability may also have caused a decrease in brightness. At the very least, it contributed to the formation of the dust cloud.

Mystery solved? Maybe, but there is another unexpected discovery of the Great Dimming.

In a new study, published Monday in the journal Nature, a trio of astronomers detail their own startling discovery: They were able to spot Betelgeuse hidden in the background of images taken by a Japanese weather satellite, Himawari-8. The chance discovery helps confirm some of the previous work revealing the origins of the Great Dimming and points to a new way to explore our cosmic neighborhood that we haven’t explored.

Himawari-8 is, as its name suggests, the eighth version of the Himawari satellite operated by the Japan Meteorological Agency. It operates in geostationary orbit, at a distance of 22,236 miles above the equator. That’s over 90 times farther than the International Space Station.

From this position, the satellite captures optical and infrared images of the entire Earth once every 10 minutes, primarily to help forecast the weather in Asia and the Western Pacific. For example, he took a ton of footage of the Tongan volcano eruption that happened on January 15. However, looking through images dating back to 2017, the trio of Japanese researchers set off in search of a hint of light that would be Betelgeuse, lurking in space behind our brilliant blue and green marble. They found it.

By studying this sting of light, the researchers came to the same conclusion as their predecessors: Betelgeuse faded due to dust and some natural variability in its light. It’s not that exciting, but it’s a good confirmation that we’re all on the right track, and that’s exactly what the scientific process is.

What’s intriguing is that a weather satellite was able to provide this data in the first place.

This could be a big problem for astronomers. Building and launching new space telescopes is not a cheap or easy undertaking and you need to reserve a rocket for yourself. But…there are already satellites orbiting Earth that might be able to do similar work.

“Himawari is like a free space telescope!” said Simon Campbell, an astronomer at Monash University in Australia.

Weather satellites like Himawari-8, for example, constantly image Earth and the space around our planet, providing mountains of data to sift through. This is important because astronomers usually have to justify the time spent on telescopes, by carving out blocks for their projects that allow them to control the focus of the telescope.

For example, when Betelgeuse mysteriously darkened, some of the most powerful ground-based telescopes were already reserved to look elsewhere. One, the Very Large Telescope in Chile, gave a team the ability to use its telescope for observations, putting off other projects. But these cases are not always checked.

So, Campbell noted, there’s a great story here about observing space. You could watch Earth imaging satellites in orbit and reuse them to study background stars. Another advantage of this is that they can observe for 24 hours and can see in additional wavelengths of light like infrared, which is blocked by Earth’s atmosphere.

Ultimately, the next time a star threatens to go supernova on us, we might already be watching.

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