The most massive stars are seldom alone. Most of them have one or more companions – stars that are bound to each other by their mutual gravitational pull. Such stars were born together, from the same giant cloud of dust and gas. Dense clumps in the cloud collapsed and split apart, giving birth to heavy stars.

One possible example is Antares, the bright star that represents the heart of Scorpius. It stands close to the left of the Moon at dawn tomorrow.

The star we see as Antares is a supergiant. It’s more than a dozen times as massive as the Sun, and hundreds of times wider. If it took the Sun’s place in our own solar system, it would swallow the four innermost planets, including Earth.

Another big star accompanies the supergiant. It’s about seven times the Sun’s mass, and five times its diameter.

But it’s unclear whether the two stars actually form a binary. They move through space in the same direction and at the same speed. But they’re separated by more than 500 times the distance from Earth to the Sun – an especially wide gap. At that range, it would take up to a couple of thousand years for the stars to orbit each other. But we’ve only known about the smaller star for a few hundred years. That’s not long enough to trace any possible orbital motion.

So while the two stars probably form a binary, the case isn’t quite conclusive.

We’ll talk about some stars that are definite binaries tomorrow.

Script by Damond Benningfield