that there is additional mass in the outer regions of galaxies that is not accounted for by the visible stars and gas. This discrepancy is often referred to as the "missing mass problem" or dark matter problem. The observed orbital velocities of stars and gas are much higher than what would be expected based on the visible mass alone. This indicates the presence of an invisible and massive component, known as dark matter, which exerts gravitational forces on the stars and gas, causing them to have higher velocities. The dark matter is thought to be spread throughout the galaxy, forming a halo-like structure that extends beyond the visible boundaries. This implies that a significant portion of a galaxy's mass is made up of this elusive dark matter, which has important implications for our understanding of the structure and formation of galaxies.
