Last month, I wrote about the star Betelgeuse and the extreme likelihood that the massive star is not about to explode. That's still probably true. If it did explode, it would actually be awesome. There aren't a lot of generations that can say they witnessed a supernova, live, with the naked eye. Unfortunately, we all know we're not the lucky ones and it will still probably be 100,000 years until the old man blows his top. Despite that, something truly weird is going on with Betelgeuse.
The excitement over a possible Betelgeuse supernova was caused by the star beginning to mysteriously dim. Some folks believed that this dimming was the beginning of the star's death throes. Once it burns out enough fuel it will collapse and as it collapses in on itself, the extreme pressure will cause a re-ignition too powerful to be held together by the dying star's gravity and it will explode in a supernova. Yet, new images of Betelgeuse show something bizarre: only part of the star is dimming.
Yep, it's gone all lumpy. Astronomers are mystified as to what could be causing this partial dimming. Betelgeuse is an old star and it burns some 2,000 degrees Celsius cooler than our sun, despite being 1.2 billion kilometers across compared to the sun's 1.4 million. Because of this, Betelgeuse is highly variable and brightens and dims on a 420-day cycle; we're now nearing the dimmest part of that cycle.
Red supergiant stars like Betelgeuse have deep convective layers where cooler gas sinks inwards towards the star's core and hot gas rises outwards. But there are also magnetic fields within the star that sometimes become tangled up and prevent the normal convective process from happening. A patch of cooler gas may stay on the outer edge of the star, dimming that part.
Betelgeuse also has stellar winds that sometimes whip up clouds of dust and minerals larger than our solar system. A thick cloud of stellar dust combined with some other factor could explain the partial dimming.
But wait, there's more. Beyond just a partial dimming, it looks as if Betelgeuse has dramatically changed shape in a very short period of time.
Betelgeuse also has an incredibly low density and doesn't exactly have a surface as the Sun does. The "surface" of Betelgeuse is more like a wispy soup. Because of this, plumes of plasma can sometimes erupt through the star and distort its appearance.
At the end of the day though, these are all just hypotheses. No one really knows for sure what Betelgeuse is doing. But the star has quickly changed appearance so dramatically that the difference is visible to the naked eye. There's one explanation, though, that has no right to be discussed but I'm going to bring it up anyway: alien megaship parked out in Betelgeuse's backyard, obscuring our view. The simplest explanation is usually the most correct, and that's simple enough to be considered stupid.