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We know from Hubble law that the galaxy is receding from each other.

Also, the general theory of relativity predicts the metric expansion of space ( voids are increasing).

Then why Andromeda is approaching the Milky Way, I think it should be going away? Where I am getting wrong?

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It is not an expanding universe of stationary balls. There is an initial velocity to astronomical objects left over from the collapse of the primordial plasma which coalesced to the present day observable universe. That space is expanding means that the velocity of andromeda towards the milky way is a tiny bit smaller than it would have been if there were no expansion.

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  • $\begingroup$ yes general relativity is bit tricky , then what about hubble law $\endgroup$ – Kunal kumar Jun 21 at 9:22
  • $\begingroup$ The law is about the motion of galaxies with respect to the earth.Individual stars have their trajectories and velocities as they wer acquired from the original coalescense of the gallaxy $\endgroup$ – anna v Jun 21 at 9:31

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