Here's why:
* Mass and Fusion: O stars are significantly more massive than G stars. Their immense gravity creates intense pressure and heat in their core, allowing them to fuse hydrogen into helium at a much faster rate.
* Fuel Consumption: The faster fusion rate means O stars burn through their hydrogen fuel much quicker.
* Main Sequence Lifetime: As a result, O stars have much shorter main sequence lifetimes, typically on the order of a few million years, compared to billions of years for G stars like our Sun.
In short, the more massive a star, the faster it burns through its fuel and the shorter its main sequence lifetime.
