Betelgeuse’s “Great Dimming” had an unlikely observer: a Japanese weather satellite

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Astronomers have a new way of studying stars: taking advantage of weather satellites orbiting Earth.

That’s the conclusion of a new paper that features new data from a Japanese weather satellite that happened to observe the red supergiant star. Betelgeuse during a period of inexplicable dimming. The chance sightings could mean a new tool for astronomers trying to figure out how a red supergiant star loses mass and eventually explodes as a supernova.

The second brightest star in orion constellation, Betelgeuse (pronounced “bet-orl-gerz” or “beetlejuice”) is the 10th brightest star in the night sky. But from October 2019 to February 2020, it dimmed dramatically to around two-thirds of its normal brightness. This so-called “big dimming” event led to speculation that it was about to explode as what scientists call a Type IIP supernova, which it will certainly do within the next 100,000 years.

Related: Orion and its dimming star Betelgeuse shine above a stargazer in this sentimental shot of the night sky

Scientists analyzing the event primarily used data from ground-based optical telescopes. Astronomers have mainly concluded that Betelgeuse’s dimming is the result of either its surface cooling, a new dust lane forming around it, or both.

Ground-based telescopes cannot see through dust and gases in the cosmos, requiring infrared vision. It’s because earth’s atmosphere blocks infrared radiation as well as x-rays, gamma rays and most ultraviolet rays. So only space observatories can see infrared light – and that includes weather satellites like Himawari-8 (opens in a new tab)one of Japan Meteorological Agency’s geostationary weather satellites.

And Himawari-8’s astrophysical debut began in an unlikely place: Twitter.

“We saw a tweet indicating the moon was in his images,” Daisuke Taniguchi, a Ph.D. student in astronomy at the University of Tokyo and first author of the paper, told Space.com. “I spoke with [third author] Shinsuke Uno on the use of weather satellites for astronomy, found that Betelgeuse is in the field of view of Himawari-8 and realized that perhaps the great dimming of Betelgeuse could be studied.”

Himawari-8 has been positioned 22,236 miles (35,786 kilometers) above Earth’s equator since 2015 to study weather patterns and natural disasters (including the eruption of the Hunga Tonga-Hunga Haʻapai volcano January 15th). Although the satellite is up there to image Earth every 10 minutes, the edges of its images include stars.

Taniguchi and his colleagues were able to see Betelgeuse in images taken throughout Himawari-8’s lifetime and measured its brightness approximately every 1.7 days between January 2017 and June 2021. And the Himawari Advanced Imager (AHI ) from the satellite studied Betelgeuse in two ways.

“In the optical and near-infrared wavelength ranges, circumstellar dust veils light from the stellar surface,” Taniguchi said, explaining that researchers — like astronomers limited to using ground-based telescopes – were able to estimate the amount of circumstellar particles. dust around Betelgeuse.

However, circumstellar dust only emits mid-infrared light. “Through the observation of such mid-infrared light, we can see the dust itself, and we can directly measure the time series of the amount of dust around Betelgeuse,” Taniguchi said. The team concluded that the “Great Dimming” in 2019 and 2020 was caused by two factors in nearly equal proportion: the star’s temperature dropped by about 250 degrees Fahrenheit (140 degrees Celsius) and the dust is condensed from the hot gas around the star.

Basically, this theory is largely in agreement with what astronomers using ground-based telescopes have concluded. For example, a study conducted by the Chinese Academy of Sciences cited the giant sunspots and temperature fluctuations while results the European Southern Observatory’s Very Large Telescope in Chile and the Hubble Space Telescope suggested Betelgeuse ejected a huge cloud of gas which cooled and condensed into dust.

Scientists’ new findings suggest that weather satellites could be used as space telescopes for astronomy. “This allows us to obtain high frame rate time series in the mid-infrared, which are difficult to acquire with usual astronomical instruments,” reads the article. In addition to not being able to record near-infrared data, ground-based telescopes lose sight of some stars for a few months as the sun drifts past them.

“It’s a possibility that I haven’t seen explored much before,” Emily Levesque, author of “The Last Stargazers” and a red supergiant star astronomer at the University of Washington, who was not not involved in the new research. com.

“It certainly depends in part on serendipity, but observations like these could prove to be a fabulous resource for nearby bright red supergiants,” she said. “Especially since they could complement the upcoming capabilities of the James Webb Space Telescopewhich is well suited to observations of darker targets.”

Observing stars in the mid-infrared is the best way to directly observe dust emissions around them, Levesque noted, because it can help create a multi-wavelength picture of massive stars and their evolution. After all, mass loss and dust production play a key role in a star’s red supergiant stage.

“Mid-infrared has also historically been difficult to observe,” she said, adding that NASA will soon be decommissioned. SOFIA the airborne observatory has filled a gap while the JWST will soon become an invaluable resource in the mid-infrared. “Combined with creative solutions like those presented in this article, we hope to continue to build a much clearer view of red supergiants in this wavelength range in the years to come.”

The authors have already started using Himawari-8 data for other stellar projects. “I believe that our concept of using a weather satellite as a space telescope is useful for several types of topics in astronomy, especially stellar astrophysics in the time domain,” Taniguchi said, referring to the emerging field focused on how astronomical objects change over time. . His group is now using data from Himawari-8 to catalog how the infrared brightness of older stars varies over time and also to search for fleeting infrared signals.

At about 548 light years (opens in a new tab), Betelgeuse is the closest red supergiant star to the solar system. It’s about 15 to 20 times the mass of the sun and about 900 times larger. If the giant were at the center of our solar system, then Mercury, Venus, Earth, Mars, and the asteroid belt would all be inside Betelgeuse.

And each time Betelgeuse goes supernova, it can shine as bright as a full moon for a few months. The end result will be a neutron star in the center of a beautiful bubble of glowing material created by the explosion. However, scientists don’t yet know exactly how a red supergiant star behaves in the weeks leading up to its explosion.

The research is described in a paper (opens in a new tab) published Monday May 30 in the journal Nature Astronomy.

Jamie Carter is the author of “A stargazing program for beginners (opens in a new tab)” (Springer, 2015) and he edits WhenIsTheNextEclipse.com. Follow him on Twitter @jamieacarter. Follow us on twitter @Spacedotcom Or on Facebook.



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