https://www.oglaf.com/allconsuminganus/

::: spoiler Alt text
use lots of lube
:::

::: spoiler Title text
there's a supermassive anus at the centre of most known galaxies.
:::

Great, now every time my kid talks about black holes, I'm going to think about supermassive anuses.

How else would a galaxy hold its angle

Some kid from a farm with a birth-mark

May be reaching... but is that a Belgariad reference? Or is that a generic trope?

Child of low social standing born with a mysterious sign, sounds like every _Chosen One_™ story. But I haven't read those in particular so maybe there's a reference I'm not seeing

True, but the MC of the Belgariad is literally a farm boy with a birthmark