© ESO/M. Montargès et al. The red supergiant star Betelgeuse, in the constellation of Orion, has been undergoing unprecedented dimming. This stunning image of the star's surface was taken with the SPHERE instrument on ESO's Very Large Telescope in January 2019, before the star started to dim. When compared with the image taken in December 2019, it shows how much the star has faded and how its apparent shape has changed. Astronomers have been warning of the dimming of Betelgeuse, the red supergiant star that acts as the shoulder of Orion in his constellation. Now, they've shared photos of the star's unusual behavior. Not only is it dimming, but its shape appears to be changing as well.
The images were captured by astronomers using the European Southern Observatory's Very Large Telescope. Currently, the star is at 36% of its normal brightness, according to researchers who observed it.
They captured photos in late December and January.
"ESO's Paranal Observatory is one of the few facilities capable of imaging the surface of Betelgeuse," said Miguel Montargès, an astronomer who led the observation team at Katholieke Universiteit Leuven in Belgium. "This is the only way we can understand what is happening to the star."
Normally one of the brightest stars in the constellation, Betelgeuse has been dimming in brightness since December.
It's a matter of when, not if, the star goes supernova -- but with Betelgeuse growing fainter over time, astronomers are theorizing it could happen very soon.
Edward Guinan, a professor at Villanova University's Department of Astronomy and Astrophysics, said that the university has been monitoring the star since 1981. It was one of his favorites to observe as a kid, so you could say Guinan has kept an eye on the star for most of his life.
Although the star experiences variability and the initial dimming was expected, it grew fainter over time rather than returning to normal brightness, Guinan said.
Astronomers, including Guinan, estimate that it could explode anytime in the next few weeks -- or the next 100,000 years.
Why the uncertainty? Because there are multiple factors we just don't know about Betelgeuse; the star is still so bright, relatively speaking, that it makes it difficult to observe and study using telescopes.
We do know that Betelgeuse is estimated to be a few million years old and is about 700 light-years away. And the "supergiant" name is no joke: According to NASA, the star is thought to be somewhere between the diameter of Mars and Jupiter's orbits in size. It's estimated to be between 11 to 12 times the mass of our sun. But neither the mass nor its distance is definite.
Factors like mass, brightness and distance can tell us how far along it is evolutionarily, Guinan said.
They expected Betelgeuse to begin dimming in December, because the star experiences periods of dimming and subsequent brightening every 425 days. And given how long it's been since the star did anything really intriguing, they were actually debating if they should keep observing it or not.
December came and the star began to dim. But instead of rising in brightness again, it has grown to become two-and-a-half times fainter, Guinan said.
They plan to keep observing the star and update the Astronomer's Telegram, which is used to alert other astronomers about potential supernovae or comets.
If they're able to see a supernova take place in real time, it would be a first. Although given its distance, we would be watching an explosion that occurred about 700 years ago.
When the supernova happens, it will appear as bright as the full moon in our sky and remain that way for weeks before declining in brightness. It would be visible with the naked eye for at least six months.
© ESO/M. Montargès et al. This image of Betelgeuse in December shows the faintness of the star, as well as a change in shape.