Some gravity particles

[imcold]

Empty while loop is worse, for sure: use TThread.WaitFor. You probably want something like this in your TPhysicsMainThread:

 
  threads: array [0..MAX_THREADS-1] of TPhysicsThread;

...
  
     stars_per_thread := count div MAX_THREADS;
        for i := low(threads) to high(threads) do
            threads[i] := TPhysicsThread.Create(FParent, i * stars_per_thread, (i + 1) * stars_per_thread - 1);
        for i := low(threads) to high(threads) do begin
            threads[i].WaitFor;
            threads[i].Free;
        end;