Learn Portuguese (Portugal): O que se passa aqui?

The normal verb passar usually means to pass, like passing by a place or passing time. Adding the reflexive pronoun se changes its meaning completely. Passar-se means to happen or to go on. If you dropped the se, the sentence would oddly mean What passes through here?

Could I say O que está a acontecer aqui? instead?

Yes, absolutely! Acontecer is the standard verb for to happen. However, passar-se is incredibly common in everyday Portuguese for asking what is going on or what is unfolding right now, especially if there is a commotion, drama, or something unusual.

Why does the se come before the verb (se passa) instead of attaching to the end (passa-se)?

In European Portuguese, pronouns normally attach to the end of the verb. However, certain words act as magnets and pull the pronoun in front of the verb. Question words like que are strong magnets. Because of the que, the se is pulled to the front, giving us que se passa instead of que passa-se.

Why does the sentence start with O que rather than just Que?