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Moon and Spica

May 15, 2019

The bright gibbous Moon stages an encounter with one of the brightest stars in northern skies tonight: Spica, the leading light of Virgo. Spica is below the Moon as night falls, and will be even closer to the Moon as they set in the wee hours of the morning.

Spica actually consists of two stars. One of them, Spica A, is more than 10 times as massive as the Sun. At that weight, it probably will end its life in a titanic explosion — a supernova.

But Spica’s fainter star is no slouch, either. Spica B is about seven times as massive as the Sun. And when you add up all wavelengths of light, it’s perhaps 2,000 times brighter. That makes it a one percenter — it’s among the top one percent of the galaxy’s biggest and brightest stars.

Spica B’s demise won’t be nearly as impressive as that of its companion, though. It’s below the weight limit that tips a star into the supernova category. Instead, its fate probably is much like the Sun’s.

As the star ages — a process that’s much faster in heavier stars like Spica B — it’ll puff up to many times its current size. Then it’ll blow its outer layers into space. That will leave only its hot, dense core — a white dwarf. And it’ll be among the galaxy’s biggest.

Of course, that scenario depends on what happens with Spica A. The two stars are quite close together, so interactions between them could alter the fate of either or both — making predictions of their future a bit iffy.

Script by Damond Benningfield

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