In: Physics
What is the evidence we have that dark matter exists within individual galaxies? In other words, exactly what observations do we make with our telescopes which tell us that there is dark matter inside individual galaxies?
Observable motions of galaxies is the evidence of unknown matter known as dark matter. This motion cann't be explained by the laws of Newtonian physics alone. We need some matter to explain galaxy rotation curve. The stars on their edges would fly away if the only thing holding them were the visible matter. Rubin estimated that the galaxies must contain about six times more mass than what could be observed with existing instruments.
Hence we have to measure galaxies rotational curve with our telescopes. It will tell us that there is dark matter inside individual galaxies. We can also see einstein ring (gravitational lensing) phenomenon for evidence of dark matter.