Four pairs of what astronomers are calling “impossible stars” — stellar twins in orbits so close they defy explanation — have been found in our Milky Way galaxy, scientists say. Astronomers using the United Kingdom Infrared Telescope in Hawaii discovered the four star pairs, each of which is a binary system in which two stars circle each other in less than four hours. Until now, scientists thought that such twin-star setups couldn’t exist.

Our sun does not orbit another star, but roughly half of the stars in our Milky Way galaxy do, as part of a binary system. These binary stars likely formed close together, and have been orbiting one another since their birth, the researchers said.