Our Sun may have a long-lost twin. Not an identical twin, but a sibling formed from the same cloud of gas and dust. Astronomers suspect that most stars, including the Sun, are born in pairs—sometimes in wide orbits that eventually separate. The hypothetical twin, called “Nemesis,” was once blamed for mass extinctions on Earth, theorized to disrupt comets in the Oort Cloud every 26 million years. No real evidence of Nemesis has been found, but the idea lingers. After all, if our Sun was born with a twin, where did it go?