Based on the science shows I watch, it seems that most contemporary astronomers believe that dark matter exists. The current estimate is that there is over 5 times more dark matter than regular matter in the universe. This is based on how much additional gravity would be required to keep galaxies together, since they would fly apart if we only counted the gravity of regular matter, as well as how much light bends when passing around these galaxies.
However, we’ve also recently learned that the solar system is far larger than we ever thought. Lots of regular matter is floating out beyond Neptune in the Kuiper Belt all the way out through the Oort Cloud. Until recently, none of this matter could be detected by our telescopes. If so, isn’t it reasonable to think that many, if not all, stars have similar clouds of matter surrounding them? If we have just begun detecting these objects, then whatever calculation was used to determine that dark matter must exist was presumably excluding all of this undetected regular matter.
We’re also starting to discover exoplanets and realizing that other solar systems are often very different than our own. Even if we ultimately learn that the matter in all the belts and bands surrounding our planetary system isn’t enough to make up the gravity gap, perhaps there is proportionally far more of this type of stuff surrounding other planetary systems.
So how certain are we that dark matter is still needed to keep galaxies stable? And even if it is, is five times still the right multiple?