Does Betelgeuse have a buddy? As in, a second star in the system orbiting around it?

It’s certainly possible, and, according to some new and interesting research, it best explains some weird behavior from the star [link to journal paper].

Betelgeuse is a red supergiant, a massive star near the end of its life. It has about 18 times the Sun’s mass, though it was likely born with more and blew away a lot of material over its lifetime, losing weight. It has definitely run out of hydrogen fuel in its core to fuse into helium and generate energy, which sets up some complicated physics that makes it swell to enormous proportions, well over 700 times the size of the Sun. It’s immense — mind you, the Sun is 1.4 million kilometers in diameter, equal to the width of over 100 Earths. Betelgeuse is the equivalent of 70,000 Earths wide. Yegads. And Betelgeuse is luminous; shining at a hundred thousand times brighter than the Sun, so that even at a distance of roughly 500 light-years from us it’s one of the brightest stars in the sky.

Famously, in late 2019 it underwent a fantastic dimming, dropping in brightness by about a factor of three, then brightening back to normal again in 2023. This is now understood to be due to a huge eruption of dust, blowing out so much carbonaceous material it blocked the light from the star. This happens with red supergiants, though the exact mechanism isn’t well understood. 

A lot of red supergiants undergo pulsations, literally brightening and dimming over time in a cycle with a fairly reproducible period. This is due to the star’s internal mechanisms, and many stars undergo pulsations. For example, if a little bit of extra heat is produced in the core it causes the star to expand a bit. As the gas expands it cools, which causes it to compress, which heats it up again, so it expands, lather rinse repeat. 

Betelgeuse, though, has two different cycles of pulsations. One is about 416 days long and the other about 2,170 days. This has long had astronomers scratching their heads trying to explain; the physics of this doesn’t make a lot of sense, and nothing seems to adequately explain both cycles.

The new paper throws a monkey in the wrench here though: the astronomers propose that the 416-day cycle is internal to the star, the natural (fundamental, as it’s called) pulsation, and the longer cycle is due to a companion star orbiting it. The 2,170-day brightness variation we see is due to the second star coming into view around the bulk of Betelgeuse itself (so the system gets brighter), then going behind it again (causing a dimming). The second star also plows through the dust around the star, excavating a hole in the cloud that lets more light through, adding to the system brightness when it’s on the near side of Betelgeuse.

This would explain a lot. They find the best fit is for a star a little more massive than the Sun, orbiting 1.3 billion kilometers out (actually, due to Big B’s size, that’s not terribly far from its surface). By itself such a star would be easy to spot from 500 light-years away, but Betelgeuse is so ridiculously luminous that its glare overwhelms the purported smaller star, making it impossible to tease out (mind you, this is separate from the idea that Betelgeuse may have had another companion star that it, um, ate). 

This does have some profound implications. Right now, given what we know of the star, we think it’s possibly past the carbon fusion stage in its core, which lasts only some hundreds of years. Each fusion stage after that takes less and less time, ending in a supernova. If true, the star only has a short time left. 

However, that assumes the long pulsation cycle is internal. If it’s actually due to a second star, then Betelgeuse is likely still fusing helium in its core, which means it has a lot longer left to go before it detonates, over a hundred thousand years. If you’re waiting for it to explode, and this second star turns out to be real, well then you’d better pack a lunch. It’ll be a while.

I enjoy debates like this in science. For one thing, Betelgeuse is a really cool star and will end with a really big bang, so it’s fun to think about. It’s also close, so when it goes it’ll be bright, outshining Venus in the sky! There’s no real threat or danger from it, so that’s a bonus. But it’s also one of the most recognizable stars in the sky, shining a dull orange-red in Orion’s left armpit (the name actually means “armpit of the giant”) during the northern winter. Yet despite its brightness, proximity, and presumed familiarity, we really still don’t understand basic features of the star. Or stars. Maybe. 

It’s a reminder not to take anything for granted, and to have an open mind to new evidence. This second star may or may not turn out to exist, but clearly there’s still a lot to learn about Betelgeuse.

I got an email from someone recently, saying they saw something pretty weird. They were watching a documentary on YouTube about Art Garfunkel and became suspicious that the narration was done by AI (I’m sure it is; I recognize the cadence and voice from a zillion AI narrated videos). Then they started wondering if the video itself was done with AI, and just as they wondered that a Very Strange Thing happened.

Here’s the video starting at 12m46 seconds. The Very Strange Thing is at 13:06.

HAHAHAHAHAHA! Oh my. No, as far as I know I am not now nor have I ever been in a duo with Paul Simon, nor would I be in any way considered an expert on such music. Just a fan. And not even a fan who knows anything, except maybe how to harmonize a little bit but only if you give a me few seconds to find the right pitch after the song starts.

So, yeah, AI. I admit this made me laugh, but in reality it sucks. That stuff is stealing licensed imagery and videos and words, and it spews out garbage like this, sometimes in a way that can be potentially fatal. I hope this fad fades soon. 

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