Will Betelgeuse blow?

Why is Betelgeuse fading? No one knows. Betelgeuse, one of the brightest and most recognized stars in the night sky, is only half as bright as it used to be only five months ago. (Illustration by ESO | L. Calcada | NASA)

With Orion’s famous star Betelgeuse still looking weirdly dim, much is being made of the possibility that it could explode into a supernova. What would that look like? What would it do to us?

Let’s review supernovae that have actually happened in our Milky Way galaxy. It’s a very exciting subject.


We now think that each galaxy experiences one or two supernovae per century, on average. When they happen, most of the time people observe a brand-new star that’s bright enough to cast shadows. And that’s with the supernova typically being thousands of light-years away. What if it were Betelgeuse, which is only around 640 light-years?

People saw supernovae in the years 1006, 1054, 1181, 1572 and 1604. That 1604 event was the last one observed in our galaxy, and the final one visible to the naked eye – until 1987. That year, a supernova went off in the nearest companion galaxy to us, the Large Magellanic Cloud. Despite its huge 750,000-light-year distance, it could be seen by the naked eye, but was too far south to be visible from the US. So, I took a small group of Woodstockers to near the Equator to see it that year.

What a thrill! It wasn’t bright, but just to observe the first naked-eye exploding star since before the telescope was invented was a fantastic experience. Two decades later, I met and hung out with the Chilean astronomer who had accidentally discovered it while casually glancing up one night: another thrill.

Anyway, the possibility, however remote, of a relatively close supernova is of course very exciting. If it were Betelgeuse, its 640-light-year distance would make it an unusually brilliant one; but that distance would be enough to protect us from all but very mild radiation exposures. It would be as bright as the Moon, with all the brilliance concentrated in a pinpoint of sky, making it almost too intense to look at. It would cast vivid shadows each night.

This possibility, though unlikely, is why, here at the Willow Observatory, I’ve been observing it spectroscopically to see if there are compositional changes that might be the first signs that something profound is happening to this suddenly enigmatic star.

Orion now looks very different from its normal appearance, since Betelgeuse is now only as bright as its belt stars. Hopefully, all readers will take a glance up to the east these nights to see this very rare phenomenon for themselves. One is reminded that the last time it got very dim (though not quite as faint as now) was in 1941. Then, amazingly, Betelgeuse not only rebounded, but attained a near-record brilliance the very next year, in 1942, when it very nearly matched the brightness of blue/white Rigel, the famous Orion foot-star. Could that happen again?

As for exploding, it could occur tonight or in 100,000 years. Hopefully it’ll be tonight.

Want to know more? To read Bob’s previous columns, click here. Check out Bob’s podcast, Astounding Universe, co-hosted by Pulse of the Planet’s Jim Metzner.

There are 3 comments

  1. Christopher Tirone

    Why do people talk about this as though it is happening now? If it “blows”, it actually “blew” 640 years ago and we’re just getting to see it now. The light that is leading scientists to suspect an imminent supernova left Betelguese 640 years ago and if a supernova did happen, it’s over already, long ago.

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