I Tidal effects of galaxies orbiting one another with dark energy?

[Suekdccia]

TL;DR Summary

Tidal effects of galaxies orbiting one another in presence of dark energy?

I recently found a question in a physics discussion site [1] about whether there was a "distance" between two galaxies where both the gravitational force and the influence of dark energy would be balanced. The answers and comments seem to indicate that there is indeed such a "radius" around a galaxy.

I was very interested in this, so I contacted the authors of this paper [2] about this phenomenon. I asked them if it could be possible to have a satellite galaxy orbiting a bigger one just in the point where there would be a balance between the gravitational attraction of the bigger galaxy and dark energy, so that the satellite galaxy orbit would not decay (through gravitational waves, tidal forces...) and avoiding its fall eventually towards the bigger galaxy.

They replied that the answer was basically yes, and that they could keep that orbit as long as there was no external perturbation modifying these orbits. But I had one more question about this scenario. My question is:

If that balanced state would be possible, would there still be tidal effects between the two galaxies (So that some of the orbits of planets and stars inside the galaxies could be somewhat modified) but without making the orbits of the galaxies decay over time...?

I mean, imagine a satellite galaxy orbits a bigger galaxy just in the radius distance where the influence of gravity and dark energy are balanced out. Is it physically possible (at least theoretically) that the tidal forces between the galaxies may affect some of the planetary systems' orbits in these galaxies (for example changing the orbits of planets around their stars like for example making them orbit their stars further apart)?

And would these tidal forces disrupt the satellite galaxy from the distance where gravity and dark energy are balanced out? Or without any external perturbation, it should keep orbiting at that distance (even with these tidal forces between the galaxies or the gravitational waves emitted from the orbits around the bigger galaxy)?[1]: https://physics.stackexchange.com/q...ional-source-where-the-influence-of-gravity-a

[2]: https://arxiv.org/abs/1206.1433

 

[256bits]

TL;DR Summary: Tidal effects of galaxies orbiting one another in presence of dark energy?

I mean, imagine a satellite galaxy orbits a bigger galaxy just in the radius distance where the influence of gravity and dark energy are balanced out. Is it physically possible (at least theoretically) that the tidal forces between the galaxies may affect some of the planetary systems' orbits in these galaxies (for example changing the orbits of planets around their stars like for example making them orbit their stars further apart)?

How much of an effect on the orbits of planets are you expecting at that radial distance?

 

[PeterDonis]

if it could be possible to have a satellite galaxy orbiting a bigger one just in the point where there would be a balance between the gravitational attraction of the bigger galaxy and dark energy, so that the satellite galaxy orbit would not decay

If there is such a balance, the smaller galaxy won't orbit the larger one. In the Newtonian picture you are using, there has to be an unbalanced inward force on the satellite galaxy for it to orbit the larger galaxy.

The paper you reference recognizes this when it says (p. 2) "The gravitationally bound system can exist only within the sphere of this radius [the radius at which the forces balance]".

If that balanced state would be possible, would there still be tidal effects between the two galaxies

Again using the Newtonian picture, this will obviously be the case in principle since galaxies are extended objects and both the ordinary gravitational force and the dark energy force will vary over the extent of the satellite galaxy. In practice the effects are likely to be quite small (the paper you reference gives formulas you can use to run the numbers if you care to).