Crimson supergiant stars are explosions ready to occur. They’re within the final stage of their life, crimson and swollen as they fuse heavier components in a final effort to maintain from collapsing. However finally, gravity will win and the crimson supergiant core will collapse, triggering a supernova. We all know it can occur, however till not too long ago, we didn’t know when.
Probably the most well-known crimson supergiant is Betelgeuse, the brilliant crimson star within the constellation Orion. It’s about 550 light-years away and has a mass of about 18 Suns. It’s the closest crimson supergiant to Earth, and when it will definitely does explode it can briefly outshine the Moon. After all, this has brought on all method of hypothesis concerning the star. Will it explode in our lifetime? Has it already exploded, and we’re simply ready for the supernova mild to succeed in us? And all astronomers have been in a position to say might be not, however we don’t actually know. However a brand new research might give us an advance warning a couple of months earlier than Betelgeuse does explode.
There are two normal fashions for crimson supergiant supernovae. Each predict a crimson supergiant ought to dim considerably earlier than exploding, on considerably totally different time scales. Within the superwind mannequin, a stellar wind is triggered by the ever-faster fee of fusion at a star’s finish of life. The outer layer of the star is pushed off by this wind over a number of many years, making a circumstellar layer of cool gasoline that causes the star to seem very dim. The fast outburst mannequin, then again, predicts a remaining interval of lower than a yr, the place greater than a tenth of a photo voltaic mass could be solid off. This may trigger the star to dim by an element of 100 inside the previous few months of its life.
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Betelgeuse solid off a darkish cloud layer in 2019, seen on this artist view. Credit score: NASA, ESA, and E. Wheatley (STScI)
On this research, the staff checked out all of the crimson supergiant supernovae circumstances the place the star was noticed earlier than its explosion. Most supernovae are solely noticed after the explosion, so between 1999 and 2017 there are solely a dozen circumstances of fine pre-supernova observations. However in all of these circumstances, the brightness of the celebrities remained pretty constant within the years main as much as the supernovae. This may rule out the superwind mannequin and suggests {that a} crimson supergiant ought to dim considerably earlier than exploding. Within the case of Betelguese, now we have seen the star dim because it solid off a cloud of gasoline, however to not the extent that signifies an eminent explosion.
Sadly, we don’t have sufficient crimson supergiant observations to have noticed a fast dimming earlier than the bang, however that might change sooner or later as extra long-term sky surveys come on-line. And who is aware of, given how well-studied Betelgeuse is, our crimson supergiant neighbor could be the primary star to present us a supernova crimson alert.
Reference: Davies, Ben, et al. “Explosion Imminent: the looks of Crimson Supergiants on the level of core-collapse.” Month-to-month Notices of the Royal Astronomical Society 517.1 (2022): 1483–1490.
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