The bizarre dimming patterns of Betelgeuse, an enormous red supergiant star in the constellation Orion, have bewildered astronomers for decades. Now, researchers are closer than ever to proving that a companion star is the cause of this strange behavior.
Researchers at the Center for Astrophysics | Harvard & Smithsonian (CfA) detected a pattern of changes in Betelgeuse using NASA’s Hubble Space Telescope and ground-based telescopes. They observed changes in the star’s spectrum—the various colors of light emitted by its composition of elements—and in the speed and direction of gases in its outer atmosphere driven by a trail of denser material.
These changes are the direct result of the companion star, Siwarha, plowing through Betelgeuse’s outer atmosphere. The dense trail the researchers observed is Siwarha’s wake, appearing just after the star crosses in front of Betelgeuse every six years.
“It’s a bit like a boat moving through water. The companion star creates a ripple effect in Betelgeuse’s atmosphere that we can actually see in the data,” lead author Andrea Dupree, an astronomer at the CfA, said in a NASA release. “For the first time, we’re seeing direct signs of this wake, or trail of gas, confirming that Betelgeuse really does have a hidden companion shaping its appearance and behavior.”
Dupree and her colleagues presented their findings during a news conference at the 247th meeting of the American Astronomical Society in Phoenix, Arizona, on Monday. The study has been accepted for publication by The Astrophysical Journal, according to NASA.
Astronomers have tracked Betelgeuse’s brightness for decades, observing two distinct periods of variation: a short 400-day cycle and a long 6-year secondary period. Their interest in the star intensified in 2020 when it suddenly dimmed to just 40% of its normal brightness, prompting renewed efforts to understand its unusual behavior.
Studies have since determined that the 2020 event, now known as The Great Dimming, was caused by a massive ejection of blazing hot material from Betelgeuse’s surface. As for the star’s periodic variations in brightness, scientists have proposed several possible explanations, including large convection cells and clouds of dust, magnetic activity, and the presence of a hidden companion star.
In recent years, astronomers have found mounting evidence to support the companion star hypothesis. In July, a team at NASA’s Ames Research Center actually managed to capture a faint image of what appeared to be the companion, nicknaming it “Siwarha.” It was the strongest evidence yet, though other experts cautioned that further observations would be needed to confirm Siwarha’s existence.
Now, Hubble and ground-based telescopes at the Fred Lawrence Whipple Observatory in Arizona and the Roque de Los Muchachos Observatory in Spain have provided those observations.
Using these telescopes, Dupree and her colleagues spent nearly eight years tracking changes in Betelgeuse’s spectrum and outer atmosphere. The patterns they observed matched what would be expected from a companion star moving through Betelgeuse’s outer atmosphere, producing a wake of disturbed gas, and aligned with the timing of Siwarha’s predicted orbit.
“The idea that Betelgeuse had an undetected companion has been gaining in popularity for the past several years, but without direct evidence, it was an unproven theory,” Dupree said. “With this new direct evidence, Betelgeuse gives us a front-row seat to watch how a giant star changes over time. Finding the wake from its companion means we can now understand how stars like this evolve, shed material, and eventually explode as supernovae.”
With that said, astronomers are still hoping to capture a clear, direct image of Betelgeuse’s buddy. They should get another chance in November 2027, when Siwarha returns to its farthest point of separation from Betelgeuse and is easiest to detect. Until then, scientists will continue to monitor the red supergiant’s behavior, looking for even more evidence of its stellar companion.
Source: Gizmodo