How do scientists know that dark matter exists?
1 Answer
Scientists invented dark matter to explain a problem. We are not sure that it exists and we certainly don't know what it is.
Explanation:
There is a problem that galaxies and groups of galaxies are spinning too fast. The gravity of the visible parts of galaxies is not sufficient to explain the speed which some stars are travelling. There needs to be a lot more material to generate the required gravity.
Dark matter was invented to explain the problem. Galaxies have large concentrations of dark matter to provide the required gravity.
Dark matter doesn't interact electromagnetically so it can't be seen. It only interacts gravitationally and possibly via the weak force.
There have been numerous ideas as to what dark matter is. Most of them require as yet undiscovered particles. It has also been suggested that it could be lots of small black holes. Alternatively it could be that our current understanding of gravity is wrong. We simply don't know at present.
