double star vs binary star

double star and binary star both are nouns.

Word	Noun	Adjective	Verb	Adverb
double star	Yes	No	No	No
binary star	Yes	No	No	No

As nouns, double star and binary star are synonyms defined as:

double star and binary star: a system of two stars that revolve around each other under their mutual gravitation

Other synonyms of double star include binary.

double star (noun)	binary star (noun)
a system of two stars that revolve around each other under their mutual gravitation	a system of two stars that revolve around each other under their mutual gravitation