# How does a nebula become a star?

Hydrogen gas at some point clumped together due to gravity and the hydrogen atoms will form a spinning cloud of gas within the nebula. Over million of years more hydrogen gas are pulled up into the spinning cloud and the hydrogen atoms collides frequently. Collisions between hydrogen atoms causes the hydrogen gas to heat up. When the temperature of the hydrogen gas reach $15 , 000 , {000}^{\circ} C$ nuclear fusion starts. And a protostar is born.