Xi Persei doesn’t look all that imposing. The star shines at fourth magnitude, so it’s visible under dark skies, but not from cities and towns. But that’s only because it’s a long way off – about 1200 light-years. In reality, it’s one of the most impressive stars visible to the human eye.
Perseus climbs the eastern sky on autumn evenings. It consists of a couple of ribbons of stars that join at Mirfak, the constellation’s leading light. And it contains the most famous variable star in the sky: Algol, the Demon Star, which fades and brightens every three days.
Yet neither can compare with Xi Persei, which is near the bottom of the longer ribbon. At visible wavelengths, it’s about 13,000 times brighter than the Sun.
But it’s tens of thousands of degrees hotter than the Sun, so it emits most of its light in the ultraviolet. When you add that in, Xi Persei is a quarter of a million times the Sun’s brightness.
The key to that showiness is the star’s mass – roughly 30 times the Sun’s mass. At that great heft, gravity squeezes its core tightly, revving up its nuclear engine. Energy works its way to the surface, making Xi Persei hot and bright.
Before long, it’ll get even hotter and brighter. It’ll explode as a supernova, briefly shining brighter than billions of normal stars – a brilliant demise for an impressive star.
Xi Persei energizes a nearby cloud of gas, and we’ll have more about that tomorrow.
Script by Damond Benningfield

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