It takes a star with the mass of the Sun approximately 10 billion years to convert all of the hydrogen in its core into helium.

Here's why:

* Nuclear Fusion: Stars like our Sun generate energy through nuclear fusion, where hydrogen atoms are fused together to form helium.

* Core Hydrogen Depletion: As the Sun continues to burn hydrogen, the core gradually becomes depleted.

* Main Sequence Lifetime: The time it takes for a star to exhaust the hydrogen in its core is called its main sequence lifetime. For a Sun-like star, this is about 10 billion years.

* Post-Main Sequence: After the core hydrogen is exhausted, the Sun will evolve into a red giant and eventually become a white dwarf.

Important Note: This is an approximate value. The actual lifetime of a star can vary slightly depending on factors like its mass and composition.