Just 548 light years from Earth, this massive red supergiant nearly 1,000 times larger than our Sun is about to explode

For generations, Betelgeuse has been one of the easiest stars to recognise in the night sky: a reddish point marking the shoulder of Orion, the Hunter. But behind that familiar glow is a huge, unstable star approaching the final stages of its life, and astronomers have now discovered that it has been hiding a stellar companion all along.

New observations with the European Southern Observatory's Very Large Telescope have produced the clearest evidence yet that Betelgeuse is part of a binary system. The finding could change how scientists understand the star's strange brightness variations, and may even complicate predictions about when it will eventually explode as a supernova.

Betelgeuse is just 550 light years from Earth

Current estimates put Betelgeuse at roughly 500-600 light years from Earth, with NASA giving an uncertain estimate of about 548 light years. That makes it one of the closest red supergiants to our planet.

Its size is difficult to pin down precisely because the star's atmosphere is enormous and turbulent, but NASA estimates its radius at roughly 724 times that of the Sun. Other measurements place its diameter at roughly 750–850 times the Sun's diameter.

If Betelgeuse replaced our Sun, its bloated outer layers would extend far beyond the orbits of the inner planets. The star is also extraordinarily luminous, radiating roughly 100,000 times the Sun's luminosity.

The red supergiant that refuses to behave

Betelgeuse is not simply large; it is remarkably volatile. As a red supergiant, it has exhausted much of the hydrogen fuel that powered it during its earlier life and has expanded dramatically.

Astronomers have watched its brightness rise and fall over different timescales. The most dramatic episode came in late 2019, when Betelgeuse suddenly became much dimmer, triggering speculation that it might be about to explode. That was not what happened.

Observations from Hubble and other telescopes showed that Betelgeuse had expelled a huge amount of material from its surface. The material cooled and formed dust, temporarily blocking part of the star's light. NASA estimates that the 2019 surface-mass ejection involved roughly 400 billion times the mass of a typical solar coronal mass ejection.

Astronomers finally see Betelgeuse's hidden companion

The newest discovery adds another mystery. For about a century, astronomers have suspected that Betelgeuse might have a companion because of unusual changes in its brightness and motion. In 2024, researchers predicted that the suspected companion would reach a position where it could be easier to see. Observations with the VLT's SPHERE instrument in December 2024 subsequently revealed a faint source next to Betelgeuse.

The suspected Betelgeuse B appears to have between 2.6 and 3.1 times the Sun's mass and orbits the supergiant at a distance comparable to Saturn's orbit around the Sun.

The companion is dramatically fainter than Betelgeuse, which explains why it remained hidden in the red supergiant's overwhelming glare. Scientists plan further observations to confirm that the object moves around Betelgeuse as expected. A follow-up observation in 2027 should provide an especially important test.

Could the companion change Betelgeuse's supernova fate?

This is where the discovery becomes particularly interesting. Betelgeuse will eventually undergo a core-collapse supernova, because massive stars cannot indefinitely support themselves against gravity once their nuclear fuel reaches the final stages of fusion. But astronomers cannot give a reliable date for the explosion.

NASA says the supernova is unlikely to occur for roughly 100,000 years, while other researchers emphasise that the exact timing remains deeply uncertain.

The newly identified companion makes that uncertainty even more significant. If Betelgeuse B is interacting gravitationally with the red supergiant, it could influence how Betelgeuse loses mass, how quickly it evolves and ultimately how its final explosion unfolds. The researchers say it is not yet known whether the companion could accelerate or delay the supernova.

What happens when Betelgeuse finally explodes?

When the star's core can no longer generate enough energy to support its enormous mass, it will collapse catastrophically. The collapse will trigger a supernova, ejecting stellar material into space and leaving behind a compact remnant, most likely a neutron star, although the precise outcome depends on how much mass remains.

From Earth, the event would be spectacular but is not expected to pose a serious threat because of Betelgeuse's great distance. NASA notes that although it would become an extraordinary celestial spectacle, the star is far enough away for Earth to remain safe.

And there is an intriguing cosmic twist: because Betelgeuse is hundreds of light years away, we are seeing it as it was hundreds of years ago. It is even possible, in principle, that the star has already exploded and that the light from the event simply has not reached Earth yet.