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More Fornax

January 20, 2017

There’s no fountain of youth to make people look younger. But there is one for stars. It’s a process that sounds like a story from a 1950s B movie — “stealing” life from another star.

A good example of a rejuvenated star is in the constellation Fornax, which is low in the south as night falls. It has only one modestly bright star, Alpha Fornacis, which is 46 light-years away.

To the eye alone, it’s not much to look at. Binoculars, though, reveal that it consists of two stars. One of them is bigger and heavier than the Sun. It’s nearing the end of its life, even though it’s almost two billion years younger than the Sun.

The other star of Alpha Fornacis is smaller than the Sun, and its surface is cooler than the Sun’s, so it glows orange. Yet it should be even redder than it is. And that’s where the story of rejuvenation comes in.

The star has been identified as a blue straggler. That means its color shifted to slightly bluer wavelengths as the star aged. It might have done so by merging with another star, which would rev up its nuclear reactions, making it hotter and bluer. On the other hand, it might have changed color by simply stealing gas from a third star in the system.

And there is some evidence of a third member of Alpha Fornacis — the corpse of a once-normal star. If it’s there, it may be about half as massive as the Sun, and quite close to the blue straggler — a dead star that gave part of its life to a stellar companion.


Script by Damond Benningfield


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