The star system known as Capella is a rarity — it contains two giant stars that are nearly identical. But the stars might not have been born so much alike. It’s possible that one of them dumped some of its gas on the other, equalizing the system. Capella is the leading light of Auriga, the charioteer. It’s in good view in the northeast by mid-evening — one of the brightest stars in the night sky. Both of its giant stars are nearing the ends of their lives, so they’ve gotten bloated. Both are about two-and-a-half times as massive as the Sun, several times the Sun’s diameter, and dozens of times its brightness. They orbit each other at about three-quarters of the distance from Earth to the Sun. But some quirks in the system indicate that things weren’t always so equal. As an example, the more massive star is locked so that the same side always faces its companion, but the companion spins much faster. That could mean that the stars were more unequal when they were born. The more-massive s
