Weather satellite accidentally tracked the mysterious fading of Betelgeuse

(ORDO NEWS) — The distant supergiant Betelgeuse accidentally fell into the lens of a spacecraft monitoring the Earth’s atmosphere, allowing us to see what was happening on it and around during the “great fading” period of 2019-2020.

The Japanese weather satellite Himawari-8 monitors the Earth, but the distant supergiant Betelgeuse also falls into its lens.

This accident brought invaluable observations of the star during the recent “great fading” – a sharp, albeit temporary drop in brightness, which has not yet been explained. The new data allowed us to test two key attenuation hypotheses and confirmed both of them.

Betelgeuse is one of the brightest stars not only in the constellation of Orion, but in the entire night sky. It is a variable red supergiant whose luminosity fluctuates over a fairly wide range.

However, in 2019-2020, astronomers noticed that the star is losing its brilliance especially strongly and sharply.

At some points, the attenuation exceeded 50 percent and was noticeable even to the naked eye. However, in 2020 everything is back to normal.

The nature of this process turned out to be incomprehensible, and many hypotheses were put forward to explain the “great decay” of Betelgeuse.

Two of them are the most respected. The first idea relates the attenuation to giant irregularities in the star itself – something like a colossal and relatively cold “sunspot” on the surface – or to a cloud of dust, plasma, which was ejected by Betelgeuse and partially eclipsed its light

Weather satellite accidentally tracked the mysterious fading of Betelgeuse 2
Changes in Betelgeuse during the “great fading” taken by the ESO VLT telescope – from the normal appearance of the star in January 2019 to the maximum decrease in brightness in the spring of 2020

To refine these calculations, observations at those wavelengths at which the presence of cosmic dust could be discerned, primarily in the near and mid-infrared ranges, would help.

The Earth’s atmosphere absorbs such radiation, so only space instruments are suitable for such work. Unfortunately, at the right time, Betelgeuse did not fall into the field of view of any orbiting telescope. At least that’s what they thought so far.

Scientists have found that the star is visible in archival data collected by the Japanese weather satellite Himawari-8 in 2019-2020.

This is a geostationary apparatus that conducts observations in the visible and infrared ranges and is oriented towards our planet.

However, at the same time, stars that are near the edge of the Earth’s disk fall into the lens. One of them turned out to be Betelgeuse, as a result of which Himawari-8 accidentally collected more than four years of observations of this supergiant.

Weather satellite accidentally tracked the mysterious fading of Betelgeuse 3
Betelgeuse was at the edge of Himawari-8’s field of view

Daisuke Taniguchi and colleagues at the University of Tokyo analyzed the data, looking for changes in size, temperature, and luminosity at different wavelengths.

The work showed that during the fading period, the surface of Betelgeuse really fell sharply – by 140 degrees. On the other hand, observations indicated an increase in the amount of dust eclipsing the star.

Japanese astronomers conclude that the extinction of Betelgeuse could be associated with both of these processes at once. Shortly before it began, the star ejected a vast cloud of plasma.

As a result of an as yet unclear process (perhaps under the action of a shock wave), this cloud cooled sharply and quickly, turning into radiation-absorbing dust.

In the same period, the temperature of the star decreased, possibly as a result of the same processes that created the shock wave.

Thus, the great damping could be associated with both dust and turbulent phenomena on the surface of Betelgeuse. However, the details of what happened are yet to be clarified.

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