Take the 2-minute tour ×
Astronomy Stack Exchange is a question and answer site for astronomers and astrophysicists. It's 100% free, no registration required.

Lets say that we observe in a distant galaxy cluster, which in all the galaxies move far away from us. and here we see in the same cluster a galaxy that move away from us in a much lower velocity than the other galaxies. is this contradict the expansion of the universe?

share|improve this question

1 Answer 1

No, it doesn't contradict the paradigm of the universal inflation. It would merely mean that the example galactic cluster that you mention has its proper (own) motion at a smaller velocity relative to the proper motion of the Milky Way than the speed of the universal inflation at the distance between them. I.e. it would move towards us, if the Universe wasn't expanding. But since it does, galactic cluster's proper motion only managed to decrease relative velocity at which it moves away from us.

To put it in analogy, say you're on a speeding train that moves at 120 km/h relative to the station it just passed by. You then lean out of its window and throw an apple towards the station that the train is now moving away from, but you can only manage to throw the apple at a velocity of 40 km/h. That apple, since it came from the train moving at 120 km/h and shared its momentum, is now travelling away from the station's platform at 80 km/h, even though you threw it towards the station, because you only managed to reduce its velocity relative to the station for 40 km/h. So it would still move away from it, but for 40 km/h slower than the train does.

share|improve this answer
thanks for the answer. but there is no need to criticize my english. not everyone is an english native speaker :) –  JekylHyde Jan 28 at 16:17
@JekylHyde I do apologize if that's how you understood it, it was not meant as a critique, perhaps more as a forenote, a fair warning that I might be missing the point in my answer because I wasn't sure I understood the nature of your question (if I did, I'd edit it for clarity instead of commenting on it). For what it's worth, I'm not a native English speaker myself. ;) –  TildalWave Jan 28 at 20:13

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.