X-ray binary stars. Composite image of a neutron star and normal star binary star pair known as Circinus X-1. This pair lies around 26,000 light years from Earth, in the Milky Way galaxy and is the youngest member of an important class of objects called X-ray binaries. X-ray binaries consist of a dense object, either a black hole or a neutron star (as here), in orbit with a star like the Sun. Researchers found that the neutron star in Circinus X-1 is less than 4,600 years old, making the X-ray binary much younger than any other known in the Milky Way. This discovery allows astronomers to study a critical phase after a supernova explosion and the birth of a neutron star. Image composed of data obtained by the Chandra X-ray Observatory (blue) and