Cougar,

I know very little about how gravity simulations are done in general, or how
grav is doing it in particular, but I suspect that it isn't practical to simulate
individual stars. There are estimated to be something like 300 billion stars
in the Milky Way, and most of the mass is supposedly in dark matter which
is spread around rather evenly. So my guess is that grav is dividing his
simulated galaxy up into a few hundred or maybe a few thousand smallish
chunks, and treating each chunk as a point mass.

Did I guess right, grav?

-- Jeff, in Minneapolis

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"The other planets?
Well, they just happen to be there, but the point of rockets is to explore them!"
-- Kai Yeves