Hydrogen

Hydrogen is the gas that powers stars. Inside a stellar core, 4 atoms of hydrogen and helium are crushed together by the immerse force of pressure to make one large atom of hydrogen. The hydrogen is then radiated through the layers of the star into space as light.

Hydrogen and lifetime of a star
A star is born in 5 types, a brown dwarf, a red dwarf, a yellow giant, a supergiant and a hypergiant and have certain amounts of hydrogen gas in their cores. A red dwarf has the largest amount of hydrogen in its core, which makes it survive for billions of years. Meanwhile, a brown dwarf is too cold for nuclear reactions to start, but it is hot enough to form a stellar core and has a minor amount of hydrogen. This makes the star last for thousands of years.