gravity between the stars energy released from the stars nuclear reactions in the stars magnetic attraction between the stars
I gave my students this multiple choice question: Binary stars orbit around the center of mass of the two stars. What causes the stars to remain together?

Only one answer is correct among these 4 choices:
- gravity between the stars
- energy released from the stars
- nuclear reactions in the stars
- magnetic attraction between the stars

Could you tell me which one is correct?

gravity between the stars