Rocks in the Way

Asteroids give the stream something to get round: a wall, a belt, a shelf.

Solid or absorbing

A rock touching a mass is the one contact test from A Star Too Heavy for Light. The mass's absorbs flag picks the ending. A black hole absorbs, so the rock is swallowed. An asteroid doesn't, so the rock crashes.

An asteroid is a GravityMass that doesn't absorb. It pulls with a mass of 40, against a hole's 450. Each level sets how big its asteroids are.