Asteroid belts are asteroids around stars
It is purely graphical it wont affect gameplay
In sectors the asteroids arent random
Even tho there are some wandering asteroids wich are randomly placed
Do i need to say more?
Many stars have the asteroid belts ( irl)
Because of physics in our universe and laws of gravity.
If there are some objects around object with higher mass the objects will form a "stable" orbit and rest will colide
Edit: i dunno if it was already in game before Dark Nebula