Here's why:

* Gravity is a fundamental force: It attracts any two objects with mass.

* Stars are massive: Stars contain a tremendous amount of matter, creating a powerful gravitational pull.

* Gravity's role in star formation: Gravity pulls together clouds of gas and dust, causing them to collapse and heat up. This heat eventually ignites nuclear fusion in the core, creating a star.

* Gravity's role in star stability: Throughout a star's life, gravity constantly pulls inward, trying to collapse the star. This inward force is balanced by the outward pressure from nuclear fusion, keeping the star stable.

So, gravity is the key force responsible for holding stars together, from their birth to their eventual death.