I am not sure to have understood the question. Let me try to answer anyways. From there, feel free to come back to me so that we could clarify your question together.

Stars do not stay in constant position. They actually move quite fast in the galaxy, at speeds easily reaching hundreds or thousands of km/s. Their motion consists of orbits around the centre of the galaxy, and the rotation speed can be measured (in the same way that Earth takes a year for one orbit around the Sun).

From this measurement (and other pieces of data), we know some invisible mass should be around (i.e. dark matter) following a certain distribution. To be precise, it forms a halo that is assumed to extend much further than the visible limits of the galaxy.

This distribution however lies all over the galaxy, and we even have a dark matter wind blowing on Earth (coming from the fact that nothing is static in the universe).

Does it help?