The multi-year pattern of dimming and brightening of the giant star Betelgeuse (don’t worry—it’s only the second time we’ve said it!) may be caused by a very small star orbiting a red supergiant, a team of astronomers reports.
The companion star, if present, is about the same mass as our Sun, and may explain Betelgeuse’s long secondary period (LSP)—a 2,170-day (6-year) cycle in which the sky dims and brightens. You see, Betelgeuse isn’t in sync with itself—its fundamental mode (or FM, that is, the main way the star beats or vibrates) is just 420 days long, much faster than the other, pulsating pattern. The latest team postulates that a second, smaller star in a binary system with Betelgeuse could be responsible for the different patterns. The research, hosted on the arXiv print server, has not been peer-reviewed.
“A friend will make both these stars move in their common place of mass, which explains the difference in speed; and will have an effect on the dust around Betelgeuse, explaining the brightness variations,” said László Mólnar, an astronomer at Hungary’s Konkoly Observatory, in an email to Gizmodo. This really changes the way we look at Betelgeuse: At first it was difficult to understand that a well-observed star could have an undiscovered companion!”
Betelgeuse is a ten-billion-odd-year-old star (a far cry from our Sun’s 5-billion-odd years) located about 642 light-years from Earth that is the brightest in the night sky. Betelgeuse is between 15 and 20 times the size of the Sun, depending on who you ask. But one fact is indisputable: a massive star is running on borrowed time, and eventually it will explode in a screaming supernova—an event that marks the end of a star’s life, save for the neutron star or black hole that usually remains behind.
You see, Betelgeuse is burning through its fuel much faster than the golden gas on which our life depends (our Sun will die in about five billion years). When Betelgeuse runs out of fuel to burn, it will eject itself, and what is left of the star will fall into a dense neutron star or black hole, depending on the amount of material that is not captured by the supernova itself.
If alpha Ori B, which our team has given the pet name ‘BetelBuddy,’ is found, it will absolutely confirm that [long secondary period] is the periodicity of 2100 days and the periodicity of 420 days is [fundamental mode]which puts 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 helium burning phase, it has about 100,000 years to go before it goes supernova.
In recent years, Betelgeuse has started doing funny things. From late 2019 to early 2020, the star dimmed to just 40% of its normal brightness—an event called The Great Dimming. Later, scientists determined that the dimming was due to a mass of surface material spewed from the star that cooled into a cloud of dust that obscured the star from observers on Earth.
Jared Goldberg, an astronomer at the Flatiron Institute and lead author of the study, told Gizmodo that some have suggested that stellar LSPs are caused by companion stars dragging dust behind them, overshadowing the giant star. However, the team found that Betelgeuse and others. stars with LSPs fade when their companion stars are behind the main star. Therefore, no dust drag can be responsible. But after considering other explanations, the team doubled down on a companion idea: Such a sidecar star (or the ‘Betelbuddy’ of our proper supergiant) could change the dust by gravity, or light it, instead of dragging it behind.
“We must remember that there have been many claims of discovery of alpha Ori B (Betelgeuse‘friend) in the 20th century,” said Miguel Montargès, an astronomer at Sorbonne Université and author of the 2021 paper The environment describing the dust covering Betelgeuse, in an email to Gizmodo. “Each one has been proven wrong.”
But “it will not be surprising Betelgeuse to have a friend,” added Montargès, who was not affiliated with the latter paper. “It is a massive star (more than 8 times the size of the sun), and statistics tell us that such stars are rarely born without siblings.”
“We all want to find out Betelgeusehis friend,” said Montargès, adding that the research “could contribute to our understanding of red supergiants.”
Last year, one team of researchers suggested that Betelgeuse would go supernova much faster than previous estimates: in just decades, or perhaps a few hundred years, instead of tens of thousands of years. But some astronomers pushed back, saying that Betelgeuse is solid in its helium-burning phase (as Joyce noted), rather than the carbon-burning core phase that would mark the supergiant’s final moments.
“The companion itself does not affect whether Betelgeuse will explode tomorrow or in the year 102024,” added Goldberg. “However, to find out a friend helps us predict better when Betelgeuse will explode.”
But it will be difficult in the end to find such a “BetelBuddy”. That’s because Betelgeuse is “incredibly, stupidly bright,” Mólnar said. “A small, sun-sized star can actually be almost invisible next to it.”
Thankfully, “almost invisible” leaves a moving, moving surface rather than a dark, literally invisible object. “To me, the most exciting thing is that we might try to use the same technology that we use to image faint planets around other stars to try to find companions around really bright stars,” Goldberg said. Some of those exoplanets are visible as they pass in front of their host stars; the planetary bodies themselves block the light seen by telescopes from the star, revealing their presence.
Additional measurements of the giant star’s brightness can be taken, but they will need to be carefully scrutinized to spot a strange Sun-sized companion amid Betelgeuse’s bright glare. However, such a discovery could also mean that Betelgeuse is not as far from burning as some have suggested.
Forget triple Betelgeuse—that’s not going to make the star finally hit the top. Also, it doesn’t really have its own cry like “Betelgeuse, Betel…buddy!”
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