Cor Caroli

When healthy twins are born, they usually have the same life expectancy. Barring accidents or disease, they should live about the same amount of time.

When twin stars are born, though, it’s a different story. One of them is likely to expire long before its sibling. And it’s pretty easy for astronomers to tell which one will go first.

Consider Cor Caroli, the brightest star of Canes Venatici, the hunting dogs. It’s in the east-northeast at nightfall. It’s the first meagerly bright star to the right of the tip of the Big Dipper’s handle.

Cor Caroli consists of two stars, which probably were born together, from the same cloud of interstellar gas and dust.

One of the stars is about three times the mass of the Sun, while the other is only half that heavy. And when it comes to a star’s life expectancy, it’s all about the mass. Heavier stars consume the nuclear fuel in the cores at a much faster rate than less-massive stars, so they expire much more quickly.

The heavier star of Cor Caroli, for example, will live as a “normal” star for about 350 million years. After that, it’ll puff up to giant proportions, shining hundreds of times brighter than it is now. Then it’ll cast its outer layers into space, leaving only its hot but dead core.

When that happens, its lighter twin will still be going strong. The more leisurely rate of nuclear reactions in its core means that it’ll shine for a couple of billion years after its flashier twin expires.

Script by Damond Benningfield