I believe that this is not the answer to dark matter, but rather “We knew how much of the universe was made up of baryonic (normal) matter, and we guessed it was intergalactic gas, and now we have measured that.”

Decades ago, astronomers estimated that “ordinary” matter (basically everything that isn’t dark matter or dark energy) makes up 5% of the universe. There was just one problem—they had no idea where most of it was.

For anyone like me who’s brain went immediately to dark matter after reading the headline, it’s related but not the dark matter itself.

Again