What does the term 'binary star system' refer to?

The term 'binary star system' refers specifically to a pair of stars that are gravitationally bound and orbit around a common center of mass. This definition highlights the dynamic relationship between the two stars, where their mutual gravitational attraction causes them to move in orbits. Binary star systems are important in astrophysics because they can provide insights into stellar masses, evolution, and distance measurements in the universe.

The first choice describes a single star with two components, which does not accurately represent the nature of a binary system that involves two distinct stars. The third choice refers to a system with three or more stars, which is known as a multiple star system, and does not apply to the definition of a binary star system. The last choice relates to a type of stellar explosion, such as a supernova, which is unrelated to binary systems. Thus, the correct interpretation of a binary star system is indeed that it involves a pair of stars that are in orbit around each other.