Moon and Spica

A bright star system with a complicated future keeps company with the full Moon tonight. Spica stands to the right or lower right of the Moon at nightfall.

Spica consists of two big, heavy stars. One is more than 10 times as massive as the Sun, while the other is about seven times the Sun’s mass.

Such heavy stars burn through their nuclear fuel in a hurry. As a result, they live much shorter lives than stars like the Sun. In fact, the heavier of Spica’s stars is already nearing the end of its “normal” lifetime. It’s beginning a series of changes that will cause its outer layers to puff up to hundreds of times the size of the Sun.

And that’s where things get complicated. The two stars are only a few million miles apart. As the heavier star gets bigger, it will dump some of its gas onto its companion. And soon after that, it’ll engulf the companion.

Under normal circumstances, the heavier star eventually would explode as a supernova. But the companion may complicate things. As the bigger star engulfs the companion, the cores of the two stars will spiral closer together. The cores may merge, hastening the explosion of the heavier one. Or they may collide more violently, setting off an even bigger blast. Or perhaps there won’t be enough time for a collision, so the heavier star will explode on its own, perhaps disrupting the smaller star.

No matter how it plays out, there’s no doubt that Spica faces an interesting future.

Script by Damond Benningfield