The red supergiant Betelgeuse, a colossal star in the constellation Orion, experienced a massive stellar outburst – unlike anything astronomers have seen before.
Betelgeuse first attracted attention in late 2019 when the star, which sparkles like a red gem in Orion’s upper right shoulder, darkened unexpectedly. The supergiant continued to dim in 2020.
Some scientists speculated that the star would explode as a supernova, and they’ve been trying to figure out what happened to it ever since.
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Now, astronomers have analyzed data from the Hubble Space Telescope and other observatories, and they believe the star may have undergone a massive surface-mass ejection, losing a significant portion of its visible surface.
“We’ve never seen a massive mass ejection from the surface of a star. There’s something going on that we don’t fully understand,” Andrea Dupree, an astrophysicist at the Harvard & Smithsonian Center for Astrophysics in Cambridge, Massachusetts, said in a statement.
“It’s a totally new phenomenon that we can observe directly with Hubble and resolve surface details. We follow the evolution of stars 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 hits Earth, it could impact satellite communications and power grids.
But the surface mass ejection that Betelgeuse experienced released more than 400 billion times as much mass as a typical coronal mass ejection from the sun.
The lifespan of a star
By observing Betelgeuse and its unusual behavior, astronomers have been able to see what happens late in a star’s life.
As Betelgeuse burns the fuel at its core, it has swollen to massive proportions and has become a red supergiant. The massive star is 1 billion miles (1.6 billion kilometers) in diameter.
Eventually, the star will explode in a supernova, an event that can be briefly visible on Earth during the day. Meanwhile, the star experiences some fiery tantrums.
The amount of mass that stars lose late in life when they burn through nuclear fusion can affect their survival, but even losing a significant amount of 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 convective plume, which is more than 1 million miles (1.6 million kilometers) wide, originated from within the star.
The plume produced shocks and pulsations that caused an eruption, peeling off a piece of the star’s outer shell, called the photosphere.
The piece of Betelgeuse’s photosphere, which weighed several times as much as the moon, was released 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 visible through observatories as well as backyard telescopes.
Recovering from the blast
Astronomers have measured the rhythm of Betelgeuse for 200 years. This star’s pulse is essentially a cycle of dimming and brightening that restarts every 400 days. That pulse has stopped for now — a testament to how consistent the eruption was.
Dupree believes the star’s internal convection cells that drive the pulsation still reverberate from the blast and likened it to the sloshing of an unbalanced washing machine tub.
Telescope data has shown that the star’s outer layer has returned to normal as Betelgeuse slowly recovers, but its surface remains resilient as the photosphere rebuilds.
“Betelgeuse continues to do some very unusual things at the moment,” Dupree said. “The interior is kind of bouncing.”
Astronomers have never 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 more follow-up opportunities to observe the mass ejected from the star using the James Webb Space Telescope, which could reveal additional clues from otherwise invisible infrared light.