You are here

Moon and Regulus

March 30, 2015

The life of a close binary system is a matter of give and take. Gas can be siphoned from one star to the other — an act that can radically change both stars.

An example is Regulus, which is the brightest star of Leo, the lion. It stands to the lower left of the Moon at nightfall.

Regulus consists of two pairs of stars. The members of one pair are small and faint. But the other pair is much more intriguing. It consists of the bright star that we see as Regulus, plus the dead core of a star that was once much brighter than Regulus itself.

Originally, this star was the more massive member of the duo, so it aged much faster. As it neared the end of its life, its outer layers of gas puffed up to giant proportions. In fact, they got so puffy that the star couldn’t hold on to them. The gravity of the other star pulled some of the gas off its surface.

As the gas fell onto the less-massive star, it transferred momentum from one star to the other. That made the star that was taking the gas spin much faster. So today, Regulus spins so fast that it bulges outward at its equator.

The process of funneling gas from one star to the other also changed the fate of the now-dead star. It lost so much gas that its corpse — a white dwarf — is much smaller than it otherwise would have been. So while one star in this famous system became bigger and brighter, the other dwindled away to almost nothing.

We’ll talk about another star in Leo tomorrow.


Script by Damond Benningfield, Copyright 2015

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.