Betelgeuse first gained attention in late 2019 when the red gem-like star on Orion’s upper right shoulder experienced an unexpected dimming. The supergiant continues to dim in 2020.
Some scientists speculated that the star would explode as a supernova, and they tried to determine what happened to it.
Now, astronomers have analyzed data from the Hubble Space Telescope and other observatories and believe the star experienced a titanic surface mass ejection, losing a significant portion of its visible surface.
“We’ve never seen a massive mass ejection on the surface of a star before. There’s something going on that we don’t fully understand,” says Andrea Dupree, an astrophysicist at the Center for Astrophysics | In a report from Harvard & Smithsonian in Cambridge, Massachusetts.
“This is a completely new phenomenon. With Hubble we can directly observe surface details. We are seeing galaxy evolution in real time.”
Our Sun regularly experiences coronal mass ejections, in which the star ejects portions of its outer atmosphere, known as the corona. If this space weather hits Earth, it will affect satellite-based communications and power grids.
But the surface mass ejection experienced by Betelgeuse was released 400 billion times more mass than the coronal mass from the Sun.
Lifetime of a star
Observing Betelgeuse and its unusual behavior allowed astronomers to see what happens late in a star’s life.
As Betelgeuse burned the fuel at its core, it swelled massively and became a red supergiant. The massive star is 1 billion miles (1.6 billion kilometers) in diameter.
Eventually, the star will explode in a supernova, which will be briefly visible on Earth during daylight hours. Meanwhile, the star experiences some fiery anger.
The amount of mass stars lose later in their lives when they burn through nuclear fusion can affect their survival. But according to astronomers, even losing a significant amount of surface mass isn’t a sign that Betelgeuse is ready to blow.
Astronomers like Dupree studied how the star behaved before, during, and after the explosion. Trying to understand what happened.
Scientists believe that a convection current extending 1 million miles (1.6 million kilometers) across originates from within the star. The plume created shocks and pulses that triggered the explosion, peeling off part of the star’s outer shell called the photosphere.
A fragment of Betelgeuse’s halo weighing several times the weight of the Moon was released into space. As the mass cooled, it formed a large cloud of dust that blocked the star’s light as seen through telescopes on Earth.
Betelgeuse is one of the brightest stars in Earth’s night sky, so its dimming — lasting a few months — is worth noting Observatories and backyard telescopes are similar.
Recovering from the blast
Astronomers have measured Betelgeuse’s rhythm for 200 years. The pulsation of this star is a dim and bright cycle that repeats itself every 400 days. The pulse has stopped for now — a testament to how consequential the explosion was.
Dupree believes the star’s interior convective cells are still reverberating from the explosion, and compares it to the sloshing of an unbalanced washing machine tub.
Telescope data Betelgeuse’s slow recovery shows that the star’s outer layer has returned to normal, but its surface remains springy as the halo rebuilds.
“Betelgeuse is doing some really extraordinary things right now,” Dupree said. “The interior is kind of hopping.”
Astronomers have never seen a star lose its visible surface before, suggesting that surface mass ejections and coronal mass ejections may be two different things.
Researchers will have more follow-up opportunities to monitor mass ejected from the star using the James Webb Space Telescope, which may reveal additional clues through invisible infrared light.
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