I like the framing of interplanetary battle just being two rude neighbors being cross with each other haha.
The gravity part felt kind of inconsistent though. Like I expected the shots to arc around the black hole in a way that makes sense, but it just seemed like the shots did whatever they wanted, especially once they started bouncing around all willy nilly. It adds to the chaos, which is fun, but it made it seem more like luck than anything else to hit your opponent.
So, all in all, cute fun game, but maybe tweak the gravity mechanics. =)