The center of mass of the solar system occasionally wanders up to 1/2 the solar diameter outside the sun. The sun rotates around this CM. Does something similar occur in spiral galaxies? If so, does a central black hole orbit around a galactic center of mass, or wobble? If so, can the effect be detected or measured? If so, would the central black hole collect more mass than if it were "motionless"?

Satellite galaxies like the Magellanic Clouds seem to me capable of supplying high non-symmetry that would enable a wobble.

  • $\begingroup$ I googled this but it does not look likewhat you are thinking. Note that the Sun has most of the Solar system's mass, while the black hole has only $10^{-5}$ of the galaxy's mass. $\endgroup$ Oct 17, 2018 at 0:32
  • $\begingroup$ My prejudice was that a spiral galaxy was like a solar system - my bad. Your answer fixed that - so, no wobble Now I wonder what holds the central black hole in the center of the galaxy, or does it wander over a large area and an irregular area?. If so, can this wandering be detected or measured? $\endgroup$ Oct 17, 2018 at 1:27
  • $\begingroup$ Is our central black hole actually at the CG of the galaxy? $\endgroup$ Oct 17, 2018 at 1:35
  • $\begingroup$ The question and answers McClary referenced are interesting and informative but incomplete. The center-of-gravity is different from the center-of-mass. The CG must vary as a galaxy's components move and irregular galaxy evolves. In the solar system the center of mass is always inside the sun. The SS's center of gravity is highly influenced by the lever arm of the gas giants and Venus and occasionally ventures well outside the sun. If the same is true in the galaxy then the SMBH may travel quite a bit near the galactic center. $\endgroup$ Oct 17, 2018 at 4:02
  • $\begingroup$ For reference I used JPL's Horizons utility to determine solar system CG vs. time. $\endgroup$ Oct 17, 2018 at 4:19


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