The yearslong dimming and brightening pattern of the huge star Betelgeuse (don’t worry—that’s just the second time we’ve said it!) may be due to a much tinier star orbiting the red supergiant, a team of astronomers report.
The companion star, if it exists, is roughly the same mass of our Sun, and may explain Betelgeuse’s long secondary period (LSP)—a 2,170-day (6-year) cycle during which the supergiant dims and brightens. You see, Betelgeuse is not in sync with itself—its fundamental mode (or FM, i.e., the primary way a star pulsates or vibrates) is just 420 days long, much quicker than this other, languid pulsation pattern. The recent team posits that a second, smaller star in a binary system with Betelgeuse could be responsible for the dissonant patterns. The research, hosted on the preprint server arXiv, is not yet peer-reviewed.
“A companion will make both stars move around their common center of mass, explaining the velocity variations; and it will have an effect on the dust surrounding Betelgeuse, explaining the brightness variations,” said László Mólnar, an astronomer at Hungary’s Konkoly Observatory, in an email to Gizmodo. “This definitely changes how we look at Betelgeuse: It was hard to grasp at first that a star this well studied might have a yet undiscovered companion!”
Betelgeuse is a 10-million-year-old star (a far cry from our Sun’s 5-billion-odd years) located some 642 light-years from Earth that’s especially bright in the night sky. Betelgeuse is between 15 to 20 times the mass of the Sun, depending on who you ask. But one fact is indisputable: the giant star is operating on borrowed time, and will eventually explode in a rip-roaring supernova—the event that marks the end of a star’s life, save for the neutron star or black hole that’s typically left behind.
You see, Betelgeuse is burning through its fuel considerably faster than the golden blob of gas on which our life depends (our Sun is slated to die in about five billion years). When Betelgeuse runs out of fuel to burn, it will expel itself outwards, and what’s left of the star will collapse into an ultra-dense neutron star or a black hole, depending on the amount of material that doesn’t get caught up in the supernova itself.
“If alpha Ori B, to which our team has given the pet name ‘BetelBuddy,’ is discovered, it would absolutely confirm that the [long secondary period] is the 2100-day periodicity and the 420-day periodicity is the [fundamental mode], which places Betelgeuse firmly in its core helium burning phase,” said study co-author Meridith Joyce, an astronomer at the University of Wyoming, in an email to Gizmodo. “If Betelgeuse is in its core helium burning phase, it has about 100,000 years to go before a supernova.”
In recent years, Betelgeuse has started acting funny. From late 2019 until early 2020, the star dimmed to just 40% its normal brightness—an event dubbed The Great Dimming. Later, scientists determined the dimming was due to a huge chunk of surface material spewed up from the star that then cooled into a dust cloud that obscured the star from observers on Earth.
Jared Goldberg, an astronomer at the Flatiron Institute and lead author of the research, told Gizmodo that some have suggested LSPs of stars are caused by faint companion stars that drag dust behind them, eclipsing the larger star However, the team found that Betelgeuse and other stars with LSPs dim when their companion stars are behind the primary star. Ergo, no dust-dragging could be responsible. But after considering other explanations, the team doubled down on the companion hypothesis: Such a sidecar star (or ‘Betelbuddy’ for our relevant supergiant) could modulate the dust gravitationally, or irradiate it, instead of dragging it behind them.
“We must keep in mind there have been several detection claims of alpha Ori B (Betelgeuse‘s companion) over the 20th century,” said Miguel Montargès, an astronomer at the Sorbonne Université and a co-author of a 2021 paper in Nature describing the dust enshrouding Betelgeuse, in an email to Gizmodo. “Each one has been proven wrong.”
But it “would not be surprising for Betelgeuse to have a companion,” Montargès, who was not affiliated with the recent paper, added. “It is a massive star (above 8 solar masses), and statistics tell us that such stars are rarely born without a sibling.”
“We all want to find Betelgeuse‘s companion,” Montargès said, adding that the research “could have implications for our understanding of red supergiants.”
Last year, one team of researchers posited that Betelgeuse would go supernova much sooner than previous estimates: in just tens of years, or maybe a couple centuries, instead of in tens of thousands of years. But other astronomers pushed back, saying that Betelgeuse is firmly in its helium-burning phase (as Joyce noted), rather than the core carbon burning phase that would mark the end times for the supergiant.
“The companion itself doesn’t impact whether Betelgeuse explodes tomorrow or in the year 102024,” Goldberg added. “However, discovering the companion helps us predict better when Betelgeuse will explode.”
But it will be difficult to ultimately discover such a “BetelBuddy.” That’s because Betelgeuse is “incredibly, stupidly bright,” Mólnar said. “A smaller, Sun-sized star can actually be almost undetectable next to it.”
Thankfully, “almost undetectable” leaves wiggle room, more wiggle room than dark matter, which is literally invisible. “To me, an especially exciting possibility is to try to use the same technology we use to directly image faint planets around other stars to try to detect companions around really bright stars,” Goldberg said. Some of those exoplanets are spotted as they pass in front of their host stars; the planetary bodies themselves block the amount of light that telescopes see from the star, evincing their existence.
More measurements of the big star’s brightness can be taken, but they’ll need to be carefully parsed to see an enigmatic Sun-sized buddy amid Betelgeuse’s brilliant glare. Still, such a discovery would also mean that Betelgeuse isn’t as far along in its burn as some have suggested.
Forget saying Betelgeuse three times—that won’t get the star to finally blow its top. Plus, it doesn’t really have as nice a ring to it as “Betelgeuse, Betel…buddy!”
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