Which of the following terms describes a binary star system in which one star emits x-rays?

The term that describes a binary star system in which one star emits X-rays is X-ray binaries. In this kind of system, the two stars are typically composed of a normal star (often a red giant or a main-sequence star) and a compact object such as a neutron star or a black hole. The intense gravitational field of the compact object pulls matter away from the normal star, and as this material spirals inwards, it heats up and emits X-rays due to the acceleration and compression of the gas.

This phenomenon is significant in studying high-energy astrophysics, as X-ray binaries are among the most luminous X-ray sources in the universe. The presence of X-rays is a key characteristic that distinguishes these systems from other types of binary stars.

On the other hand, while neutron stars, red dwarfs, and white dwarfs are types of stellar objects, they do not specifically define a binary system that emits X-rays. Neutron stars may be found in X-ray binary systems, but the term on its own does not convey the binary nature or the emission of X-rays stemming from the interaction with another star.