There is strange activity going for the last few months [leading up to November 2021] on Betelgeuse. First doubted as supernova and later cosmic or cosmological dust.
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6$\begingroup$ For the "last few months" betelgeuse has been not strange at all. mag 0.5 in visible aavso.org/LCGv2 $\endgroup$– James KCommented Nov 6, 2021 at 4:44
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$\begingroup$ Question seems perfectly clear and has been nicely answered. Closing as "unlcear" makes no sense. voting to leave open $\endgroup$– uhohCommented Nov 14, 2021 at 10:55
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2 Answers
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Recently (for about a year) Betelgeuse has been very stable, without any significant dimming or brightening (See its light curve, type "Betelgeuse" into the search box). There has been no strange activity. Indeed the only thing "strange" is the last few months is how stable it has been!
In 2019 there was a period of significant dimming. This was due to an outburst that released material into its atmosphere. This material condensed to form dust that blocked the light. There aren't now any "competing theories". Supernova was never seriously considered.
Betelgeuse is variable, and undergoes pulsations that change its brightness. There are also large "starspots", cooler regions on its surface, that can change the effective brightness of the star as they rotate to face us. It had been suggested that an exceptionally deep pulsation, or a very large starspot, or perhaps a combination of several factors at once could have combined to cause the dimming in 2019.
See the results from Hubble: Hubble Finds That Betelgeuse's Mysterious Dimming Is Due to a Traumatic Outburst
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$\begingroup$ A follow-up on that, did we actually see clear spectral dust signatures (such as the 9.6 $\rm \mu m$ SiO-feature)? $\endgroup$ Commented Nov 7, 2021 at 16:49
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There were certainly other theories to explain Betelgeuse's dimming. The big one is that perhaps there was a dark (cold) spot on the star. That's known as a "convective cell" (recall that the envelopes of stars are convective) and a cold spot would be darker in the visible electromagnetic regime.
