A few months before the COVID-19 pandemic really started in early 2020, the world was fixed on a distant supergiant star, some 700 light-years away, known as Betelgeuse. The monstrous furnace suddenly dimmed, becoming 10 times darker than usual. Some suggested it was the start of an explosion, but rumors of the star’s demise were greatly exaggerated. Only a few months later it glowed.
After several teams tried to explain what caused this “Great Dimming,” one team analyzed hundreds of images of the star to reveal stardust, possibly obscuring our view from Earth. In June 2021, they showed that Betelgeuse had probably ejected gas, which then cooled and condensed and darkened the star. Another group suggested that the star was also cooling slightly and that this variability may have resulted in a decrease in brightness. At least, it contributed to the formation of the dust cloud.
Mystery solved? Perhaps, but there is another unexpected discovery from the Great Dimming.
In a new study published Monday in the journal Nature, a trio of astronomers details their surprising discovery: They were able to spot Betelgeuse lurking in the background of images taken by Himawari-8, a Japanese weather satellite. The grim discovery helps confirm some of the earlier work uncovering the origins of the Great Dimming and points to a new way to explore our cosmic neighborhood that we haven’t explored.
Himawari-8, as the name suggests, is 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 from the equator. It is 90 times farther from the International Space Station.
From that position, the satellite snaps optical and infrared images of the entire Earth once every 10 minutes, primarily to help forecast weather across Asia and the western Pacific. For example, it snapped up a ton of images of the Tongan volcanic eruption that occurred on January 15. However, looking at images taken as far back as 2017, a trio of Japanese researchers went looking for a prick of light that would be Betelgeuse, the secret space behind our brilliant blue and green marble. He found it.
Studying that prick of light, the researchers came to the same conclusion as their predecessors: Betelgeuse dimmed both because of the dust and some natural variability in its light. It’s not all that exciting, but it’s good confirmation that we’re all on the right track, and that’s exactly the process of science.
Interestingly, a weather satellite was able to provide this data in the first place.
This could be a big deal for astronomers. Building and launching new space telescopes is not a cheap or easy endeavor and you’ll have to book yourself a rocket. But… there are already satellites orbiting the Earth that may be able to do the same thing.
“Himawari is like a free space telescope!” Simon Campbell, an astronomer at Monash University in Australia, said.
For example, weather satellites like Himawari-8 are constantly imaging Earth and the space around our planet, providing mountains of data to filter through. This is important because astronomers usually have to make a case for timing on telescopes, creating blocks for their projects that allow them to control where the telescope is focused.
For example, when Betelgeuse mysteriously dimmed, some of the most powerful telescopes on the ground were already booked for viewing elsewhere. One, the Very Large Telescope in Chile, gave a team the opportunity to use their telescopes for observation, leaving other projects behind. But these cases do not always come up.
So, Campbell said, here’s a neat story about seeing space. You can see Earth imaging satellites in orbit and reuse them to study background stars. Another advantage of this is that they can observe for more than 24 hours and be able to see in additional wavelengths of light, such as infrared, which is blocked by Earth’s atmosphere.
Ultimately, the next time a star threatens to go supernova on us, we’ll already be watching.