Last week, scientists at Caltech announced that they'd found direct evidence of the intergalactic medium (IGM) made up of "dim matter," the faint, wispy mix of hot gas filaments (marbled, perhaps, with invisible dark matter) that links all galaxies together. And it's hard to overstate the importance of this finding, in terms of scale; we've discovered the cosmic web, the bones of the universe.
This animation from the National Center for Supercomputing Applications' Advanced Visualization Laboratory (AVL) shows how galaxies form in the swirling cosmic mist:
The discovery of the gas filaments that make up the cosmic web has elicited a relatively tame media response because scientists have long suspected its existence, and journalists don't tend to have much to say about uncontroversial findings that confirm what was already suspected—but depending on what it tells us, it may ultimately turn out to be one of the most significant scientific discoveries of the century. From looking at this cosmic web, we can plainly see that the galaxies that we think of as isolated chunks of matter floating helplessly in the ineffably massive open void of dark, silent space are actually touching each other—clinging, in a sense, to each other—as the universe continues to expand.