You are here

More Moon and Companions

December 19, 2011

The Moon, the planet Saturn, and the star Spica form a bright triangle at first light tomorrow. Saturn is to the upper left of the Moon, with Spica about the same distance to the upper right of the Moon.

Although it looks like a single point of light, the star that we see as Spica actually consists of two stars. Both of them are much hotter, brighter, and heavier than the Sun. But they’re locked in a tight orbit that makes them impossible to see as individual stars.

Because the stars are so big, heavy, and close together, they exert a strong gravitational tug on each other — so strong that each star causes the other to bulge outward. Seen in profile, the system would look like two eggs with the narrow ends pointed at each other.

In the next few million years, the heavier star will near the end of its “normal” lifetime. It’ll puff up to many times its current size. As it swells, some of its gas will begin to dump onto the surface of the other star. And as it gets even bigger, its outer layers will engulf its partner, pulling the two stellar cores closer together.

No one knows exactly how the scenario will play out after that. The stars may merge to form a single star. Or the larger star may explode before that can happen, blasting itself to bits and perhaps sending its companion careening through the galaxy like a stellar bullet.

No matter what happens, though, it’s clear that Spica is in for an exciting future.


Script by Damond Benningfield, Copyright 2011


Get Premium Audio

Listen to today's episode of StarDate on the web the same day it airs in high-quality streaming audio without any extra ads or announcements. Choose a $8 one-month pass, or listen every day for a year for just $30.