I’ve always been a strong skeptic of DARK MATTER! theories. A non-believer, if you will, probably because skepticism is my base state.
The original “discovery” of DARK MATTER! was because the stars of the Milky Way don’t rotate around the galactic center properly. The stars out toward what we thought to be the edge of the disk rotated too fast, in violation of the known laws of gravity. They rotated just as if there was more unseen mass further out from the core, and I do admit one thing: The velocities of stars do not lie. That matter is out there.
Scientists, just like cavemen, don’t like to leave things unexplained. Since we couldn’t see the matter surrounding the galaxy, it must be <key spooky music> DARK MATTER! <said in scary movie announcer voice>
The fact is that we simply don’t know enough to make that supposition. That sound in the dark? The caveman thought it was the ghosts of their ancestors, and within a few tellings of that reason it was gospel truth. The stars are moving too fast? Must be DARK MATTER! and within a few studies that made DARK MATTER! seem reasonable… well, you know how that works. Inertia is just as strong in scientists as it is in cavemen.
But look! We’ve discovered more mass to the galaxy. Potentially 60% more mass. And I predict that’s just the start. Andromeda has a dark (but detectable) halo of matter around it that makes Andromeda 6x larger, and 1000x times more massive… WOW!
Would that much mass explain the rotation rates? I bet it would. I bet that someday we discover the Milky Way has the same halo of matter and increase in mass. When that happens, we will be able to do away with the concept of DARK MATTER! and realize that the universe is much more WYSIWYG than we though. (What you see is what you get.)