The star that marks the heart of the lion has received a giant gift from a companion star. That gift has completely changed both stars.

Regulus is below the Moon as night falls this evening, and even closer to the Moon as they set, in the wee hours of the morning.

The star we see as Regulus is called Regulus A. It’s much bigger, brighter, and heavier than the Sun. But it’s even more impressive now than when it was born. That’s because it has a close companion that was heavier than Regulus. More-massive stars die more quickly. As they die, they puff up. So as the companion expired, it began dumping gas onto Regulus A. That made Regulus A much bigger and heavier.

Those weren’t the only effects, though. The surface of Regulus A got much hotter and brighter. That made the star look at least a billion years younger than it really is.

As gas flowed in from the companion, it also made Regulus A spin much faster. Today, it rotates once every 16 hours. By comparison, it takes almost a month for the Sun to rotate. So Regulus A bulges out at the equator.

Finally, the surface of Regulus A has a higher concentration of “metals” than the Sun does – elements other than hydrogen and helium. Many of the heavier elements were forged in the heart of the companion, then dumped onto the surface of Regulus A – one of many changes triggered by a now-dead stellar companion.

We’ll have more about the metals in stars tomorrow.

Script by Damond Benningfield