The red supergiant Betelgeuse, a colossal star in the constellation of Orion, experienced a massive stellar flare – never seen before, according to astronomers.
Betelgeuse first caught attention in late 2019 when the star, which shimmers like a red gem in Orion’s upper right shoulder, experienced an unexpected darkening. The supergiant has continued to darken in 2020.
Some scientists speculated that the star would explode as a supernova, and they are trying to figure out what has happened to it since.
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Now astronomers have analyzed data from the Hubble Space Telescope and other observatories, and they believe the star suffered a titanic surface mass ejection, losing a substantial portion of its visible surface.
“We have never seen a huge mass ejection from the surface of a star before. We end up with something 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 completely new phenomenon that we can directly observe and resolve surface details with Hubble. We observe stellar evolution in real time.
Our sun regularly experiences coronal mass ejections during which the star releases parts of its outer atmosphere, known as the corona. If this space weather hits Earth, it can impact satellite communications and power grids.
But the surface mass ejection that Betelgeuse experienced released more than 400 billion times more mass than a typical coronal mass ejection from the sun.
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The life of a star
Observing Betelgeuse and its unusual behavior has allowed astronomers to observe what happens late in a star’s life.
As Betelgeuse burns fuel in its core, it swells to massive proportions, becoming a red supergiant. The massive star is 1 billion miles (1.6 billion kilometers) in diameter.
Eventually, the star will explode into a supernova, an event that might be briefly visible during the day on Earth. Meanwhile, the star is experiencing fiery temper tantrums.
The amount of mass that stars lose late in their lives when they burn up by 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 the astronomers.
Astronomers like Dupree studied how the star behaved before, during and after the flare in an effort to figure out what happened.
Scientists believe a convective plume, spanning more than a million miles (1.6 million kilometers) in diameter, originated from inside the star.
The plume created shocks and pulsations that triggered an eruption, peeling off a piece of the star’s outer shell called the photosphere.
Betelgeuse’s piece of 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 light from the star 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 backyard telescopes.
Recover from the explosion
Astronomers have measured the rhythm of Betelgeuse for 200 years. The pulse of this star is essentially a dimming and brightening cycle that restarts every 400 days. This impulse has ceased for the time being – a testament to the magnitude of the eruption.
Dupree thinks the star’s inner convection cells that drive the pulsation still resonate from the explosion, and has compared it to the sloshing of an unbalanced washing machine tub.
Telescope data showed that the star’s outer layer has returned to normal as Betelgeuse slowly recovers, but its surface remains elastic as the photosphere rebuilds.
“Betelgeuse continues to do some very unusual things right now,” Dupree said. “The interior is kind of bouncy.”
Astronomers have never seen a star lose so much of its visible surface before, suggesting that surface mass ejections and coronal mass ejections could be two very different things.
Researchers will have a better chance of tracking the star’s ejected mass using the James Webb Space Telescope, which could reveal additional clues through otherwise invisible infrared light.