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To modern eyes, the stars of Sagittarius form the outline of a teapot. But in Greek mythology, the constellation was far more extensive. It represented a centaur – half-man, half-horse – holding a bow and arrow. And the brightest star in the constellation plays a role in both of those pictures.
Kaus Australis is at the lower right corner of the teapot. It also represents the southern end of the bow – in fact, that’s the meaning of its name.
It’s actually a binary – two stars in a wide orbit around one another. One of the stars is like the Sun. But from the system’s distance of about 145 light-years, it’s much too faint to see with the eye alone.
The star we can see is much bigger and heavier than the Sun, and about 500 times brighter. And it spins in a hurry – once every 1.6 days, compared to almost four weeks for the Sun. If it were spinning just a little faster, it would rip itself apart. In fact, it’s closer to that self-destruct point than any other star yet seen.
As a result of its rotation, the star is squashed – it’s about a third wider through the equator than the poles. And because they’re closer to the star’s core, the poles are thousands of degrees hotter than the equator.
Astronomers can’t explain the star’s high-speed rotation. The star could be siphoning gas from a much-closer companion that’s hidden from view – spinning up the tip of the archer’s bow.
Script by Damond Benningfield
