Well, are they then the ‘missing mass’ being looked for.
Makes a lot of sense, solves a lot of problems.
And now seems we don’t know much about nothing...er...vacuums.
No, the “missing mass” is most likely not missing at all, it’s just a plug they have used to make their faulty equations match up better with observed reality.
Basically, if reality behaved according to the way the math predicts, then the spiral arms of galaxies would rotate slower than the center of the galaxy. Instead, we see the arms rotating at the same speed. The physicists try to wallpaper over this problem by saying their could be a bunch of mass conveniently hidden just where they need it, in order to accelerate the spiral arms to just the right speed. The entire idea, though, is patently ludicrous.