Betelgeuse: is it about to explode?

The fair timescale

Betelgeuse is a red supergiant, roughly 15 to 20 times the Sun's mass, late in its life. It will collapse and explode.

The uncertainty is huge because we can't see the core. Estimates commonly put the explosion within about 100,000 years. It could already have happened, with the light still on its way, since the star is 500 to 700 light years off.

'Astronomically imminent' means something very different from imminent. A star that has lived ten million years with 100,000 left is in the last 1% of its life. That's late. The chance of it going in your lifetime is still tiny.

Betelgeuse is not about to explode. I'd stop reading any article that says it is.

The Great Dimming

Between late 2019 and early 2020 Betelgeuse faded dramatically, dropping to around 40% of its usual brightness, enough to visibly alter Orion to the naked eye. Speculation about an imminent supernova followed immediately.

The explanation turned out to be dust. The star ejected a substantial cloud of material which cooled and condensed into dust, obscuring part of the surface from our viewpoint. Imaging showed the southern portion of the disc darkened rather than the whole star fading uniformly, which pointed to obscuration instead of a change in output.

A local surface cooling episode probably contributed. Either way it was an episode of a variable star doing what variable stars do, not a countdown.

It remains a practical case study in reading astronomical news: a unusual observation produced enormous speculation, and the mundane explanation took months to establish.

Betelgeuse is not about to explode, and I'd stop reading any article that says it is.

Betelbuddy

Betelgeuse has long shown a roughly 2,170-day brightness cycle that no model of the star alone explained well. In 2023 researchers argued from over a century of observational data that a companion star could account for it.

In December 2024 that companion was imaged for the first time, using speckle imaging on a large telescope. Informally nicknamed Betelbuddy, it appears to be a young star of roughly 1.4 to 2 solar masses, around the Sun's size instead of the stellar remnant many had expected.

The proposed mechanism is that the companion's orbit periodically clears away obscuring dust, letting Betelgeuse appear brighter on that cycle.

Its long-term fate is striking: the companion is expected to spiral inward and merge with Betelgeuse, possibly within about 10,000 years, plausibly before the supernova.

Observing it

Betelgeuse is the bright orange-red star marking Orion's shoulder, and its colour is obvious to the naked eye: a genuine contrast with blue-white Rigel at the opposite corner.

It is a semi-regular variable, changing brightness by several tenths of a magnitude over months. You can track this yourself by comparing it with nearby stars of known brightness, which is one of the more accessible forms of real amateur science.

It is also one of very few stars whose disc has been resolved. It is enormous (if placed at the Sun's position it would extend past Mars) and imaging shows an irregular, asymmetric surface with convection cells far larger than the entire Sun.