For decades, Regulus had astronomers fooled. The star is bright, hot, and blue – an indication that it was quite young. Most estimates put its age at no more than a hundred million years – about two percent the age of the Sun. Instead, it’s at least a billion years old. But like a vampire, it’s been rejuvenated by taking the life’s blood of a companion, making it look much younger.

The star we see as Regulus is about four times the size and mass of the Sun, and more than 300 times brighter. A few decades ago, astronomers discovered its companion – a “dead” star known as a white dwarf. The two stars are so close together that the corpse was hidden in the glare of the bright star.

The presence of the companion means the system has to be at least a billion years old – old enough for the companion to evolve to its present state. As it evolved, it puffed up. Gas flowed from its surface over to the other star. That made the star we see today much bigger and heavier. It also made the star hotter, which made it bluer. Hot blue stars usually are quite young. So astronomers were fooled into thinking that bright Regulus was still a youngster – not an older star that’s been rejuvenated.

Look for Regulus close to the Moon at dawn tomorrow. The distance between them will narrow as you move westward. They’ll be especially close as seen from Alaska or Hawaii.

Script by Damond Benningfield