Your friendly neighbourhood supergiant!

Good old Betelgeuse. There aren’t many stars close enough that you can actually image them as more than just a point of light. Also known as Alpha Orionis, Betelgeuse is so big and so nearby though, that ESO’s VLT (Very Large Telescope) can image it quite easily. Using some funky adaptive optics chicanery, they managed to glean this stunning image, showing plumes of starstuff being cast off into the night. Plumes that could easily engulf our solar system.

Betelgeuse is actually one of the largest stars known (although it’s still only about half the size of the mighty VY Canis Majoris). Stars like these aren’t going to last much longer. So massive they’re used up most of their fuel, their cores start fusing heavier elements. As a result, they bloat into monsters. Monsters with low surface gravity. We know that stars like these lose huge amounts of material to the space around them, because we can see it. Astrochemists like me find them pretty fascinating, because all of that stellar material can have some pretty exotic chemistry. All the same, the fine details of how these stars shed their skin aren’t entirely clear.

In truth, it’s no great surprise that Betelgeuse isn’t losing material uniformly in all directions. The old entry I linked to above shows that VY CMa is much the same. All the same, imaging Betelgeuse in such detail has allowed a group of plucky astronomers to discover, for the first time, that the surface of a red supergiant like Betelgeuse is a seething, roiling mass. To look at, it would appear as if the star itself was actually boiling. Actually, this also makes a lot of sense. A red supergiant would be low in density, so it would be highly convective (like red dwarfs are). That convection wcould cause magnetic fields and possibly drive mass loss. Maybe something like a gargantuan version of Solar coronal mass ejections.

Such a variable surface could also have something to do with recent reports of Betelgeuse appearing to have shrunk. All the same, a reduction in size of about 15% in as many years is a little surprising. Seemingly, no one’s quite sure if it’s some kind of long term variability in the star, or if it’s the beginning of the end for it. On the other hand, with such an uneven bubbly surface, and an extremely slow rotation rate (the star spins once every 18 years or so), perhaps we just happen to be looking at a thin part of it. There’s even a chance that those plumes of gas enshrouding the star might have been confusing matters.

In any case, there’s still an incredible amount we don’t know about stars. Even the most mundane stars out there. Hell, there’s a lot we still don’t know about our own star, the Sun. Red giants and supergiants, as they near the end of their lives, are a big unknown. Which makes it rather helpful to have a conveniently placed behemoth like Betelgeuse for us to take a closer look at!

Telescope image: ESO and P. Kervella
Artists Impression: ESO / L. Calçada


About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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6 Responses to Your friendly neighbourhood supergiant!

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