Betelgeuse first came to attention in late 2019 when the star, which shines like a red gem on Orion’s upper right shoulder, underwent an unexpected dimming. The supergiant continued to darken in 2020.
Some scientists speculated that the star would explode as a supernova, and have been trying to determine what happened to it ever since.
Now, astronomers have analyzed data from the Hubble Space Telescope and other observatories, and believe the star underwent a titanic surface mass ejection, losing a substantial part of its visible surface.
“We’ve never seen such a large mass ejection from the surface of a star before. We’re left with something we don’t fully understand,” said Andrea Dupree, an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, in a statement.
“It’s a totally new phenomenon that we can directly observe and resolve surface details with Hubble. We’re looking at stellar evolution in real time.”
Our sun regularly experiences coronal mass ejections in which the star releases parts of its outer atmosphere, known as the corona. If this space weather reaches Earth, it may have an impact on satellite communications and power grids.
But the surface mass ejection that Betelgeuse experienced released more than 400 billion times the mass of a typical coronal mass ejection from the sun.
the life of a star
The observation of Betelgeuse and its unusual behavior has allowed astronomers to observe what happens at the end of a star’s life.
As Betelgeuse burns the fuel in its core, it has swollen to massive proportions, becoming a red supergiant. The massive star is 1.6 billion kilometers (1 billion miles) in diameter.
Ultimately, the star will explode in a supernova, an event that could be seen briefly during the day on Earth. Meanwhile, the star is experiencing some tantrums.
The amount of mass that stars lose at the end of their lives as they burn up through nuclear fusion can affect their survival, But even losing a significant amount of its surface mass is not a sign that Betelgeuse is ready to explode, according to astronomers.
Astronomers like Dupree have studied how the star behaved before, during and after the eruption. in an effort to understand what happened.
Scientists believe that a plume of convection, stretching more than 1.6 million kilometers (1 million miles) across, originated in the star’s interior. The plume created shocks and pulsations that triggered an eruption, shedding a chunk of the star’s outer shell called the photosphere.
The chunk of Betelgeuse’s photosphere, weighing several times more than the moon, was launched into space. As the mass cooled, it formed a large cloud of dust that blocked the star’s light when viewed through telescopes on Earth.
Betelgeuse is one of the brightest stars in Earth’s night sky, so its dimming, which lasted a few months, was noticeable through observatories and garden telescopes alike.
Astronomers have measured Betelgeuse’s rhythm for 200 years. The pulse of this star is essentially a cycle of dimming and brightening that restarts every 400 days. That pulse has ceased for now, a testament to how important the eruption was.
Dupree believes that the convection cells in the star’s interior that drive the pulsation are still reverberating from the explosion, comparing it to the sloshing of an unbalanced washing machine tub.
telescope data has shown that the star’s outer shell has returned to normal as Betelgeuse slowly recovers, but its surface remains elastic while the photosphere rebuilds.
“Betelgeuse continues to do some very unusual things right now,” Dupree said. “The interior is like bouncing.”
Astronomers have never before seen a star lose so much of its visible surface, suggesting that surface mass ejections and coronal mass ejections could be two very different things.
Researchers will have further follow-up opportunities to observe the ejected mass of the star using the James Webb Space Telescope, which could reveal additional clues via otherwise invisible infrared light.
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