Thanks. Yeah, there are a couple of glitches in there. The ships bounce off the edge of the screen, and smaller ships run from bigger ones -- combined, that makes them crawl along the sides. Looping around is a good idea, or I'm wondering if there could be some kind of log scale to distance the further out from the centre the ships get. I did a variation a while back with a star in the middle that could be tweaked for that (click to add a ship). Mind you, the gravity from the star pretty much takes care of that problem.

http://codepen.io/simonswain/full/cKejC/

> Maybe make it so they loop back

That's be a toroidal spacetime surface, wouldn't it? Would gravitational influence also have to "loop around" the borders?

If not, you might get some very interesting effects if a mass is near the edge of the map.