[rw]

> biggest energy source of our galaxy

You meant the Sun, of course. However, your phrasing sent me on a quest to answer the galactic question. From the following article, I learned that the "supermassive black hole at the centre of the Milky Way" emits "cosmic radiation at petaelectronvolt energies", which fits the bill for largest energy source of our galaxy.

https://www.mpg.de/10390310/acceleration-petaelectronvolt-pr...

[Retric]

On the other hand if your looking at energy by type, fusion wins hands down.