Until Ostriker and Gnedin's simulations, it was an unanswered question. Physicists postulated that supernovas somehow blasted matter the enormous distances required to deposit it between the galaxies. The simulations show another way. Almost immediately after reionization, stars begin to gather in small groups, forerunners of present-day galaxies. Drawn by each other's gravity, some of these protogalaxies merge, and in the swirling tango of merger, some of their gas breaks away, thrown into space at high velocities.
Heavy elements have a choice now.
They can drive or take the bus. Before there was no choice. This mechanism wasn't noticed till now, and you can notice it only with a simulation. It's a good example of how large-scale computation can give a qualitatively new result. Another conclusion from the simulations is that these protogalaxies formed at the end of the dark ages are similar in their fundamental internal properties to galaxies we see around us.