Talk about cheek to cheek. These two ancient stars are both burned-out relics of suns once about the size of our own. And they've spiraled in so close that they orbit each other every 5.4 minutes and occupy a space only about 100,000 kilometers wide—about a quarter the distance between Earth and the Moon. Astronomers report this week in The Astrophysical Journal Letters that the pair, called HM Cancri and located about 16,000 light-years away, represents the smallest and closest-orbiting binary system ever found. The team also suspects that HM Cancri might help them confirm the existence of gravity waves, an elusive phenomenon that Einstein theorized can happen when rapidly spinning massive objects generate ripples through space-time.