In a Scientific American article about galaxies and dark matter halos, the author says :
These dark matter halos are believed to have acted as gravitational sinks for normal matter, seeding the subsequent formation of galaxies in the early universe. The telltale motions of the stars they shepherd betray their endurance to this day. Such halos still surround galaxies like our own, majestic-but-invisible sculptors of the modern cosmos.
I can't get the likeness between halos and sculptors?