Which of the following is a tightly bound physical system, likely to endure for many billions of years?

Question

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A binary star system consists of two stars orbiting around a common center of mass, held together by their gravitational attraction. This is a tightly bound system that can last for billions of years. Open clusters, stellar associations, and OB associations are all loose collections of stars that are not as tightly bound and may disperse over time.

Which of the Following Is a Tightly Bound Physical System