Remember when Betelgeuse dimmed dramatically in late 2019 and early 2020, sparking speculation that the supergiant star might be about to explode? Researchers at Harvard think they've figured out what's really going on—and it involves a companion star we've never directly observed.
Betelgeuse is a red supergiant in the constellation Orion, roughly 650 light-years away. It's one of the brightest stars in our night sky and destined to end its life in a spectacular supernova. The question has always been: when?
The 2019-2020 dimming event—when the star faded to about 40% of its normal brightness—was unprecedented in modern observations. Initial theories suggested massive dust clouds ejected from the star's surface, or perhaps convection cells (think stellar weather patterns) blocking light. Subsequent observations supported the dust hypothesis for that particular event.
But Betelgeuse has other oddities. Its rotation is unusually fast for a star of its size and evolutionary stage. And its brightness variations don't follow simple patterns—there are multiple overlapping cycles at different timescales.
Enter the companion star hypothesis. If Betelgeuse has an unseen stellar companion in orbit around it, the gravitational interaction could explain both the rotation anomaly and the complex brightness variations.
Here's how: A companion star's gravity would tidally interact with Betelgeuse's outer layers, potentially spinning up the star's rotation over time. The orbital motion could also periodically disturb Betelgeuse's atmosphere, triggering enhanced mass loss and dust formation at specific points in the orbit—creating quasi-periodic brightness dips.
The companion wouldn't need to be particularly massive or bright. A smaller star in an elongated orbit, passing close to Betelgeuse periodically, could do the job while remaining undetected in the overwhelming glare of the supergiant.
Detecting such a companion directly is challenging but not impossible. Future observations using interferometry or careful monitoring for gravitational perturbations might reveal the hidden star. If confirmed, it would fundamentally change our understanding of Betelgeuse's evolution.
What about the supernova prediction? A companion wouldn't prevent the eventual explosion—Betelgeuse has already fused most of its core hydrogen and helium and is burning heavier elements. When the core collapses, the star goes supernova regardless of what's orbiting it.
But the companion affect the timeline. Binary interactions can alter mass loss rates and internal mixing, potentially accelerating or delaying core collapse. So the presence of a companion might actually help us better predict when Betelgeuse will explode—whether that's 100,000 years from now or tomorrow.
