Astronomers are revisiting long-standing assumptions about the iconic red supergiant Betelgeuse, one of the brightest stars in the night sky, as a new study suggests it might not be a single star but part of a binary system.
This research proposes that Betelgeuse could be accompanied by a smaller, sunlike companion, which may help explain some of the puzzling behaviors observed in the star, such as its periodic dimming and brightening. If confirmed, this discovery would have profound implications for how we understand massive stars nearing the end of their life cycle.
A Companion Star Behind Betelgeuse’s Mysterious Brightness Fluctuations?
The idea of a companion star has been proposed as a solution to one of the most perplexing phenomena in Betelgeuse’s behavior: its long secondary period (LSP). Betelgeuse exhibits a pulsation cycle every 400 days, during which it dims and brightens as the star swells and contracts. However, Betelgeuse also experiences a much longer six-year cycle (2,170 days), which astronomers have struggled to explain. This longer cycle, coupled with events like the dramatic “Great Dimming” of 2020, has led researchers to explore the possibility that a second, smaller star could be responsible for these anomalies.
The recent study, led by astronomers Jared Goldberg from the Flatiron Institute and Meridith Joyce from the University of Wyoming, proposes that this unseen companion, which they’ve affectionately dubbed “Betelbuddy”, could be interacting with Betelgeuse’s dust clouds, affecting how much light reaches Earth. As Joyce explains, “When the companion star sails into view of Earth, it temporarily disperses the clouds of dust surrounding Betelgeuse,” which causes Betelgeuse to appear brighter from our perspective. This interaction between the companion and the surrounding dust could account for the star’s irregular brightness changes, particularly during its LSP.
The Nature of Betelbuddy: Sunlike Star or Neutron Star?
While the companion star is theorized to be sunlike, some researchers, including Joyce, believe it could be something more exotic, such as a neutron star—the ultradense core left behind after a massive star collapses in a supernova. However, this idea is complicated by the fact that astronomers have not observed the X-ray emissions typically associated with neutron stars. “We would expect to see evidence of this with X-ray observations, which we haven’t,” Joyce noted, casting some doubt on the neutron star hypothesis.
The team’s calculations suggest that Betelbuddy could be up to two times the mass of the Sun, though this is not definitive. What makes this discovery so intriguing is that Betelgeuse, a massive star around 15 to 20 times the mass of the Sun, is nearing the end of its life. It is expected to go supernova in the distant future, and understanding whether it has a companion could provide vital clues about its exact evolutionary stage. As Joyce points out, “If Betelgeuse is in its core helium-burning phase, it has about 100,000 years to go before a supernova.” This places Betelgeuse in a relatively calm phase of its life cycle, contrary to some earlier predictions that suggested the star could explode within the next few centuries.
Detecting Betelbuddy: A Technological Challenge
One of the main challenges in confirming the existence of a companion star is Betelgeuse’s overwhelming brightness. The red supergiant is located about 642 light-years from Earth and is one of the most luminous stars in the night sky, making it difficult to spot a smaller, dimmer companion nearby. László Molnár, an astronomer at Hungary’s Konkoly Observatory and a co-author of the study, acknowledged this difficulty, saying that Betelgeuse is “incredibly, stupidly bright.” This brightness effectively blinds telescopes to the presence of a smaller star, especially one that might be close in mass to the Sun.
Despite this, Molnár remains optimistic, stating that the potential for spotting Betelbuddy lies in using techniques similar to those applied in the detection of exoplanets. These methods involve observing tiny dips in brightness as a smaller object passes in front of its larger companion. As Jared Goldberg, the lead author of the study, noted, “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.”
Detecting a sunlike companion would help explain why Betelgeuse’s brightness changes are so erratic and would also offer new insights into its internal dynamics, particularly its core. Although the star’s current phase has been well studied, the influence of a second star could alter our understanding of how massive stars like Betelgeuse live out their final stages before exploding in a supernova.
Implications for Understanding Red Supergiants
The discovery of a companion star orbiting Betelgeuse would have significant implications for our understanding of red supergiants and the final stages of massive star evolution. Red supergiants like Betelgeuse are known for their instability as they near the end of their lives, but the presence of a companion could introduce additional complexities to how these stars behave. As Miguel Montargès, an astronomer from Sorbonne Université not affiliated with the study, noted, “It would not be surprising for Betelgeuse to have a companion. It is a massive star, and statistics tell us that such stars are rarely born without a sibling.”
Montargès also emphasized that, while earlier attempts to detect a companion have proven unsuccessful, this new research offers a fresh perspective on how Betelgeuse’s behavior might be influenced by another star. “We all want to find Betelgeuse’s companion,” Montargès said, adding that doing so “could have implications for our understanding of red supergiants.”
Beyond just solving the mystery of Betelgeuse’s dimming, confirming a companion could help scientists better predict when the star will eventually go supernova. While Betelgeuse’s companion, if it exists, doesn’t directly impact the timing of this cataclysmic event, it may provide a more precise understanding of the star’s evolutionary timeline. As Goldberg put it, “Discovering the companion helps us predict better when Betelgeuse will explode.”
What’s Next for Betelgeuse?
The possibility that Betelgeuse could be a binary system is still a hypothesis, and further observations will be needed to confirm it. Joyce and her team are currently working on proposals for future observations, with a potential window for new data coming in December. These observations will aim to provide the direct evidence needed to validate the existence of Betelbuddy, which would be a game-changing discovery in the study of massive stars.
For now, Betelgeuse remains one of the most mysterious stars in our galaxy, and the question of whether it is accompanied by a smaller star continues to intrigue astronomers. As technology advances, the ability to observe faint objects near bright stars like Betelgeuse will improve, bringing us closer to solving one of the biggest mysteries in stellar astrophysics.