Today's FLASH experiments ended in disaster again, but not as much disaster as the last attempt. Making the ambient medium a thousand times less dense seems to have helped. Now the disc stays respectably stable for about 400 Myr, at which point it... err... well it does something wrong. It doesn't collapse, or explode, or tear itself to shreds... I don't know how to describe it. Watch for yourself, it's very pretty.
The problem may be that the boundary of the simulation is too small. FLASH abhors a vacuum, so there has to be some ambient medium (albeit of arbitrarily low density) and a specified computational volume. Early on, the disc expands just a little bit and brushes against the edge of the simulation volume. Then it collapses again. To fill in the gap that would be left by the collapsing gap, FLASH inserts gas of equal density to the gas that last contacted the edge. That may be causing a runaway effect, since the mass at the end of the simulation is 100 times the mass at the start. Ooops.
No fair! Why is it when I fail a programming I get stack traces, but you get awesome looking pictures, astronomers
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