In the Earth-Moon system tidal-friction slows down the rotation, so does it do the same for the galaxy?

  • If not how come, and why it's different than on Earth?

  • If so can this slow-down be the reason for collapse of the matter to quasars? If not why?

Sorry if this is a silly question but I was not able to find anything on Google.

  • $\begingroup$ Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. $\endgroup$
    – Community Bot
    Commented Nov 9, 2022 at 7:17

1 Answer 1


Tidal friction is caused by big objects that can "feel" gradient in the gravitational field of another object. It works for moon, because it's diameter is close to the distance from Earth to Moon. Moon deformation requires energy that goes from orbital rotation. But objects, orbiting galaxy has too small sizes to feel gradient of galaxy's gravity field.

If so can this slow-down be the reason for collapse of the matter to quasars? If not why?

Yes it can, the difference in matter's orbital velocity make friction that consumes orbital energy, but it's not the only reason of collapse. Near the black holes gravity field is so big, that another parts of Taylor expansion appears, field is not only $1/r^2$ anymore and orbits become unstable.

  • $\begingroup$ The distance to the moon is more than 100 times its diameter. Is this close enough to one for current purposes? $\endgroup$
    – D. Halsey
    Commented Nov 10, 2022 at 0:15
  • $\begingroup$ it's enough for weak influence of field dradient that can be detected. On the other side, the sizes of sun diameter for ex. are $10^{12}$ times smaller than galaxy diameter $\endgroup$ Commented Nov 10, 2022 at 15:36

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