The enormous star known as Betelgeuse has been a target of study since the early days of astronomy. As one of the brightest objects in the sky, it’s visible even without a telescope. But in 2019, it dimmed considerably. With the aid of the Hubble Space Telescope, scientists from the Harvard-Smithsonian Center for Astrophysics have identified a cause: an unfathomably large Surface Mass Ejection (SME), which is something we’ve never observed before.
The scale of this monstrous star can be hard to fathom. It’s almost 20 times the mass of our sun, but it’s nearing the end of its short lifespan as a red supergiant. If you were to replace the sun with Betelgeuse, it would completely engulf all the inner planets, as well as the asteroid belt.
The sun regularly pitches a fit and launches bubbles of stellar material into space; an event known as a Coronal Mass Ejection (CME). The Surface Mass Ejection (SME) from Betelgeuse identified by Hubble blasted around 400 billion times as much material into space. It’s no wonder the effects were detectable from hundreds of light years away. Following the SME in 2019, the star decreased in brightness three-fold.
Generally, the more massive a star, the faster it burns through its nuclear fuel. Betelgeuse is already long in the tooth at around 10 million years old. Before exploding in a supernova, red giant stars begin losing mass, and the SME in 2019 may be a part of that process. No one can say for sure yet because this is all new. “We’ve never before seen a huge mass ejection of the surface of a star,” said astronomer Andrea Dupree. “We are left with something going on that we don’t completely understand. It’s a totally new phenomenon that we can observe directly and resolve surface details with Hubble. We’re watching stellar evolution in real time.”
Dupree has assembled data from Hubble, as well as other observatories like the STELLA robotic observatory and NASA’s STEREO-A to get a picture of what happened to Betelgeuse. The outburst was possibly the result of a convective plume, which would have begun deep in the star before rushing to the surface. The violent process essentially blasted a hole in the photosphere, which produced a cloud of starstuff more than a million miles across. As it sped away from the star and cooled, the star’s light was partially blocked.
The dimming of Betelgeuse was apparent with the naked eye, and it lasted months. What’s more, the star’s reliable 400-day brightness cycle has been disrupted, demonstrating just how catastrophic this event was. No one expects Betelgeuse to explode in a supernova anytime soon, and when it does, our solar system is far enough away to avoid ill effects. It’ll be a spectacular light show, though.
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