X-ray binaries are a type of binary star system where one star is a compact object, such as a black hole or neutron star, and the other is a normal star. The compact object pulls material from the companion star, creating an accretion disk. As the material spirals in, it heats up and emits X-rays, which can be detected by telescopes. These systems are important for studying extreme physics and the behavior of matter under intense gravity. They also help astronomers understand the life cycles of stars and the formation of black holes and neutron stars.