Historically, one of the brightest stars in our sky has been Betelgeuse, a red supergiant located in the constellation of Orion. But late last year, astronomers noticed something strange about this familiar sight — it was dimming dramatically. It’s not unusual for stars to fluctuate between higher and lower levels of brightness, but in this case, the fluctuations were purely in one direction and extremely rapid. This lead many in the astronomical community to wonder if Betelguese may soon go supernova, reaching the end of its life and exploding in an enormous outburst.
Now, astronomers using the European Southern Observatory’s Very Large Telescope (VLT) have shown the dimming of this star with two images taken almost a year apart. The big news is not only that the star is dimming — it’s now down to just 36% of its typical brightness, which is noticeable even with the naked eye — but also that its shape is changing.
The ESO astronomers don’t think that the dimming is related to an impending supernova, however. Instead, they think it is due to one of two possibilities. The first possibility is that, because Betelgeuse has an irregular surface consisting of enormous convection cells, these cells are moving, shrinking, or growing in a way that changes the brightness of the star. Alternatively, the star could be ejecting matter away from its core in the form of dust, creating clouds that block our view of its light.
“The two scenarios we are working on are a cooling of the surface due to exceptional stellar activity or dust ejection towards us,” Miguel Montargès, an astronomer at KU Leuven in Belgium, explained in a statement. “Of course, our knowledge of red supergiants remains incomplete, and this is still a work in progress, so a surprise can still happen.”
The VLT is armed with another instrument to study Betelgeuse during this unexpected dimming event, using the infrared wavelength as well as the visible light wavelength. The star has been imaged using VISIR, the VLT Imager and Spectrometer for mid-Infrared, which shows how the dust surrounding the star glows due to heat and radiation.
The process of shedding dust happens throughout the lifetime of stars like this one, with material being pumped out into space and eventually forming new stars.
“The phrase ‘we are all made of stardust’ is one we hear a lot in popular astronomy, but where exactly does this dust come from?” says Emily Cannon, a Ph.D. student at KU Leuven, said in the statement. “Over their lifetimes, red supergiants like Betelgeuse create and eject vast amounts of material even before they explode as supernovae. Modern technology has enabled us to study these objects, hundreds of light-years away, in unprecedented detail giving us the opportunity to unravel the mystery of what triggers their mass loss.”