Limerick Astronomy Club: Betelgeuse could be near its end

Orion is the most easily recognizable constellation in the winter sky standing as it does high in the south just after sunset.

The star Betelgeuse stands out in Orion as it is the second brightest star in the constellation and it has a dark red colour. Or at least it was the second brightest star in Orion (and the tenth brightest in the sky). Since last October it has become a lot dimmer, by January of this year it had dropped to almost a third of its usual brightness and had lost a lot of its red colour too.

Betelgeuse is a type of Star called a red supergiant. These stars are much more massive and brighter than our sun, Betelgeuse is about 10 times heavier and 100,000 brighter than the sun. But supergiants burn through their fuel much faster than smaller stars and so have much shorter "lifespans", Betelgeuse is less than 10 million years old and is coming to the end of its life, compare that to our sun which at 4.5 billion years old is half way through its life.

This is the reason there was so much excitement at Betelgeuse dimming, some observers saw it as a sign that the star was about to die and we would get a ringside seat to a supernova: the immense explosion that marks the end of a giant stars life. The problem with predicting the death of a star is that there are so many variables to consider and while it was generally expected that the end would come sometime in the next 100,000 years, it would require lotto levels of luck if this was going to happen in our lifetime.

One of the reasons for scepticism about the possibility of a supernova is that Betelgeuse is known to be a variable star, so it does change brightness over time. And while the changes this time were more than expected, the timing for the dimming fits with usual variation in brightness. So since the middle of February the dimming has stopped and according to some observations there may even be a slight brightening.

There is also another reason arguing against a supernova soon: while there is a big change in brightness in visible light, there is not much difference in the infrared part of the spectrum. This suggests that whatever is happening, it is not the radical change in the structure of the star that we would expect if it was dying. The latest theory is that dust is streaming away from the star and this is responsible for the dimming we are seeing.

Limerick Astronomy Club email limerickastronomyclub @gmail.com