Here's the breakdown:
* Nebulas are giant clouds of gas and dust. These clouds are mostly made up of hydrogen and helium, with trace amounts of other elements.
* Gravity causes the gas and dust to clump together. Over time, these clumps get denser and hotter.
* Eventually, the core of a clump becomes so hot and dense that nuclear fusion begins. This is the process that powers stars, where hydrogen atoms fuse to form helium, releasing enormous amounts of energy.
So, it's not about the *number* of nebulas but rather the *density* and *mass* within a nebula that determines if a star will form.
Think of it like this:
* Imagine a cloud of smoke. If the smoke is spread out thinly, it will just dissipate. But if the smoke condenses and forms a dense cloud, it can become visible and even block out light.
* Similarly, nebulas need to become sufficiently dense and massive for gravity to pull the material together and ignite nuclear fusion, creating a star.
