Betelgeuse is a red supergiant, one of the largest types of stars in the universe. To give a sense of scale, if Betelgeuse were placed at the center of our solar system, its surface would extend beyond the orbit of Jupiter. At around 700 times the size of the Sun and over 10,000 times brighter, it has long captivated stargazers with its brilliance.
Yet, there’s a reason why this cosmic giant stands out in the night sky — it’s nearing the end of its life. Stars like Betelgeuse burn through their fuel much faster than smaller stars like the Sun. Having already fused most of its hydrogen, Betelgeuse has entered a more advanced stage of stellar evolution, one that could lead to its collapse and a supernova explosion — a rare and spectacular event that will be visible from Earth even during the day.
In the last few years, Betelgeuse began to dim only to rise back in brightness — and so again in pulsating cycles. At first, many thought the star might be about to explode.
Now, a team of researchers suggests that an unseen companion star — affectionately dubbed the “Betelbuddy” — may be the key to understanding these mysterious pulses.
A Hidden Star in Plain Sight
For years, scientists have observed that Betelgeuse doesn’t shine steadily. Instead, it pulses, getting brighter and dimmer in two distinct cycles: a shorter one lasting around 420 days and a longer one spanning about six years. The cause of this longer cycle, known as the long secondary period, has been a puzzle.
“We ruled out every intrinsic source of variability that we could think of as to why the brightening and dimming was happening in this way,” said Jared Goldberg, the study’s lead author and a research fellow at the Flatiron Institute’s Center for Computational Astrophysics. “The only hypothesis that seemed to fit is that Betelgeuse has a companion.”
The team’s research proposes that the Betelbuddy — a star up to twice the mass of our sun — orbits Betelgeuse in a binary system. As it does, it interacts with the vast clouds of dust that Betelgeuse expels, affecting how much of the star’s light reaches Earth. This could explain the longer pulsation cycle.
Implications for Betelgeuse’s Fate
Understanding what’s causing Betelgeuse’s pulsations could also help predict when the star might explode.
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Astronomers gauge a star’s life stage by its pulsation modes. If the 420-day cycle is Betelgeuse’s fundamental mode — a pattern intrinsic to the star — it suggests the star is in a stable phase, burning helium in its core. This means it might not go supernova for another 100,000 years.
“Nothing else added up,” Goldberg said. “Basically, if there’s no Betelbuddy, then that means there’s something way weirder going on —something impossible to explain with current physics.”
Detecting the Betelbuddy won’t be easy. Betelgeuse’s brilliance makes it extremely challenging to spot a smaller, dimmer star nearby.
“A smaller, sun-sized star can actually be almost undetectable next to it,” explained László Molnár, a co-author of the study and an astronomer at Konkoly Observatory in Hungary. The team plans to search for direct evidence of the companion around December 6, when there may be a window of visibility.
“We need to confirm that Betelbuddy actually exists, since our result is based on inference, not on direct detection,” Molnár said. “So we’re working on observation proposals now.”
A Star Full of Surprises
Betelgeuse has been in the lens of astronomers for centuries, yet it continues to surprise us. In late 2019 and early 2020, the star underwent an unusual dimming event, leading some to speculate that it might be about to explode. Later investigations revealed that the dimming was due to a cloud of dust released by the star itself.
“Betelgeuse has been the target of countless studies since the dawn of modern astrophysics,” Molnár noted. “And yet there’s still room to make significant new discoveries: in this case, a sunlike star hiding in plain sight, in the immense glare of a red supergiant.”
The discovery of the Betelbuddy could refine predictions about when Betelgeuse will meet its fiery end. While some earlier studies suggested the supernova might happen soon, this new research implies we may have much longer to wait.
“The companion itself doesn’t impact whether Betelgeuse explodes tomorrow or in the year 102,024,” Goldberg said. “However, discovering the companion helps us predict better when Betelgeuse will explode.”
As they await new observations, the team — and the wider astronomical community — looks forward to uncovering more secrets from one of the sky’s most famous stars.
The findings appeared in The Astrophysical Journal.