Moon and Companions

The Sun isn’t bothered by much. That’s because it orbits the center of the galaxy on its own. But most of the stars in the galaxy have at least one companion star. And the interactions between them can have a big impact.

Consider Spica, a bright star near the Moon tonight. Although it looks like a single star, it really is at least two stars. One of them is more than 11 times the mass of the Sun, while the other is about seven times the Sun’s mass. That makes Spica one of the most impressive binary systems around.

Its stars are extremely close together. They follow a stretched-out orbit that brings their surfaces to within about 10 million miles of each other.

So the stars have big impacts on each other. For one thing, their mutual gravitational pull distorts both stars. They’re shaped like eggs, with the tapered ends pointing toward each other. Also, the pull of the smaller star appears to create ripples in the larger star. And the sides of the stars that face each other are hotter than the sides that face away.

In a few million years, the larger star will explode as a supernova. That’s likely to blast away some of the gas at the surface of the companion. And it’ll probably send the smaller star zipping across the galaxy -- fired into space by a close companion.

Look for Spica to the lower right of the Moon at nightfall. The much brighter planet Jupiter is about the same distance to the lower left of the Moon.

More tomorrow.

Script by Damond Benningfield