The Mystery of Betelgeuse’s Dimming Has Finally Been Solved



In December 2019, astronomers observed an odd, dramatic dimming within the gentle from Betelgeuse, a brilliant pink star within the Orion constellation. They puzzled over the phenomenon and puzzled whether or not it was an indication that the star was about to go supernova. A number of months later, they’d narrowed the almost definitely explanations to 2: a short-lived chilly patch on the star’s southern floor (akin to a solar spot), or a clump of mud making the star appear dimmer to observers on Earth. We now have our reply, in accordance with a brand new paper printed within the journal Nature. Mud is the main wrongdoer, however it’s linked to the transient emergence of a chilly spot.

As Ars’ John Timmer reported final yr, Betelgeuse is among the closest huge stars to Earth, about 700 gentle years away. It is an outdated star that has reached the stage the place it glows a uninteresting pink and expands, with the new core solely having a tenuous gravitational grip on its outer layers. The star has one thing akin to a heartbeat, albeit a particularly sluggish and irregular one. Over time, the star cycles via intervals when its floor expands after which contracts.

Considered one of these cycles is pretty common, taking a bit over 5 years to finish. Layered on that could be a shorter, extra irregular cycle that takes wherever from underneath a yr to 1.5 years to finish. Whereas they’re straightforward to trace with ground-based telescopes, these shifts do not trigger the form of radical modifications within the star’s gentle that might account for the modifications seen in the course of the dimming occasion.


In late 2019, Betelgeuse dimmed a lot that the distinction was seen to the bare eye. The dimming persevered, reducing in brightness by 35 % in mid-February, earlier than brightening once more in April 2020.

Telescopes pointed on the large had been capable of decide that—quite than a tidy, uniform drop in luminance—Betelgeuse’s dimming was erratically distributed, giving the star an odd, squished form when seen from Earth. That raised a lot of questions on what was occurring with the large, with some consultants speculating that due to Betelgeuse’s measurement and superior age, the unusual conduct was an indication of a supernova within the making.

By mid-2020, astronomers had modified their tune. A world staff of observers occurred to have the Hubble Area Telescope pointed at Betelgeuse earlier than, throughout, and after the dimming occasion. Mixed with some well timed floor observations, this UV knowledge indicated {that a} huge burp that fashioned a cloud of mud close to the star could have prompted the star to get darker.

“With Hubble, we might see the fabric because it left the star’s floor and moved out via the ambiance, earlier than the mud fashioned that prompted the star to look to dim,” mentioned Andrea Dupree, an astronomer on the Harvard-Smithsonian Heart for Astrophysics who made these observations. She can also be a co-author on the brand new paper.

{Photograph}: M. Montargès et al./ESO


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