Most of the world was concerned with a fading point of light more than 500 light-years away in the late 19th century. Betelgeuse, the red supergiant star easily recognizable as the right shoulder of the constellation, had suddenly and mysteriously faded away. It was thought to be on the verge of exploding as a supernova, an event otherwise predicted to occur within 100,000 years. By early February of 2020, the fading had stopped, and within weeks the star had returned to its normal brightness, which left researchers with unanswered questions.
The answers came from a number of different places. A team of researchers who had used the Hubble Space Telescope to observe Betelgeuse before, during and after the event reported that a massive ejection of hot material from the star had created an obscuring cloud of dust. The temperature of Betelgeuse plummeted by at least 170 kelvins during the Great Dimming due to a very large, relatively cool dark. Another team used the Very Large Telescope to conclude that both scenarios were correct. The emergence of a dark spot in the star's southern hemisphere had lowered surrounding temperatures and created a bubble of hot gas. The Great Dimming was created from a starlight-blocking dust cloud that formed as it cooled.
A camera on a weather satellite has entered the mix. Three graduate students at the University of Tokyo took a closer look at archival images captured by the satellite during the Great Dimming after realizing that Betelgeuse appears in the field of view. Their results, published in Nature Astronomy, support the twofold hypothesis and raise the possibility that data from other meteorological satellites may be used for a broad range of astronomy observations. The study of Himawari-8's images has inspired the National Oceanic and Atmospheric Administration to look into whether one of its own satellites can duplicate the findings.
An astronomer at the Harvard-Smithsonian Institute for Astrophysics is familiar with the research. I really like the result. The earlier study that used Hubble data to link the Great Dimming to Betelgeuse burping out a dust cloud was met with a lot of debate.
Dupree has used unconventional methods in the past. During the summer months, Betelgeuse is so close in the sky to our star that the glare from telescopes makes it hard to see it. It is possible to have an unimpeded view from a telescope in the solar system. Dupree wanted to get another look at Betelgeuse during the summer, so he contacted officials at NASA to ask to use the STEREO-A satellite. Dupree says she wouldn't have thought of using a meteorological satellite.
The idea to use Himawari-8 data came about through a social media post. A post about Earth's moon photobombing some of Himawari-8's images caught the attention of the lead author. The weather satellite could be used to observe Betelgeuse. The idea was intriguing because of a number of benefits. Ground-based telescopes suffer from the Earth's atmosphere and can't see many parts of the wavelength range. The competition to get observation time on space telescopes is very severe.
Taniguchi reached out to fellow graduate student and study co-author Kazuya Yamazaki to see if they could make their own observations. The stars in Himawari-8's images are very dark compared to the moon. Yamazaki and Taniguchi decided to try.
Betelgeuse is easy to see when it falls within Himawari-8's field of view. Its chances of being registered in meteorological satellite detectors, which are not designed for astronomy, are boosted by being bright at both optical and IR wavelength. It's one thing to find a star in satellite images, but it's another to use the data to make high-precision stellar measurements. Data-wrangling was the most time consuming part of the study.
The Himawari-8 result inspired Dupree to get the help of Jon Fulbright, a scientist at the product quality team at NASA. Fulbright is still trying to get insights on Betelgeuse from the GOES-R data and is grappling with burdensome unit conversions and resizing required for the task He says that the benefits of using an unconventional data source may not be worth the drawbacks.
I'm not sure if it's a one-time thing or not. For this novel approach to reach its full potential, better methods must be developed to bridge the gaps between meteorological and astronomy data sets. New generations of Earth-observing satellites should be designed with them in mind. He thinks that something like this will get people thinking.
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