Stars don't actually "combine together" in the way that we might think of two objects merging. Instead, the process is more about nuclear fusion, which happens within the core of a star. Here's a breakdown:

* Gravity's Role: Stars form from massive clouds of gas and dust called nebulae. Gravity pulls this material together, causing the cloud to collapse and heat up.

* Core Formation: As the cloud collapses, the core becomes incredibly dense and hot. The pressure at the core becomes immense.

* Nuclear Fusion Ignition: At a certain point, the pressure and temperature in the core become so extreme that atomic nuclei (mostly hydrogen) are forced to overcome their natural repulsion and fuse together.

* Energy Release: This fusion process releases a tremendous amount of energy, which is what makes stars shine. It also creates heavier elements, like helium.

* Hydrostatic Equilibrium: The outward pressure from fusion balances the inward pull of gravity, keeping the star stable.

So, it's not about stars combining physically, but about the nuclear reactions occurring within their cores.

Here are some additional points:

* Stars don't combine to form larger stars: The process of star formation involves the collapse of a single nebula.

* Stars can be part of multiple-star systems: Stars can be gravitationally bound to each other, forming binary systems or even larger groupings. However, they don't fuse together in this case.

Let me know if you have any other questions about stars!