# Null points between galaxies

• wolram
In summary, there are Lagrange points between gravitationaly bound galaxies, but they rely on specific assumptions that may not apply to these galaxies. These points are based on the mathematics of the Newtonian two body problem and are typically found in binary galaxy systems or even larger scales. However, the assumptions of point particles or spherical objects in orbit around a common center of mass may not apply to these galaxies on a collision course. Therefore, while there may be a Lagrange point 1, it may not be a point but rather an extended region of low potential.

#### wolram

Gold Member
Dearly Missed
Are there large scale lagrange points between gravitationaly bound galaxies?
ie a small galaxy that orbits a larger one, or even points where gravity is null
between near large bodies

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Lagrange's calculation is based on very general (but also very specialized) mathematics, in particular the Newtonian two body problem. So yes, there should be the same old 5 lagrangian points for the Milky Way and the Andromeda galaxy, since they are a reasonably good approximation to a two body system. Similarly for any other more or less isolated binary galaxies. Also true at even larger scales if you can find binary galaxy clusters or even bound binary superclusters. (I'm not aware of any, but that doesn't mean they don't exist.) Probably even more similar points exist in three and more body systems, but this is much more complex mathematics and I am not aware of any general results.
Best, Jim

Lagrange points rely on two assumptions. The first is that the bodies are point particles or spherical, since the external gravitational field of a spherical object is the same as the field or a point particle of the same mass. The second is that the objects are in orbit around a common centre of mass.

The first probably dosn't apply to these galaxies, and the second doesn't either. They are on a collision course rather than an orbit. If you look at the main image inhttp://en.wikipedia.org/wiki/Lagrange_points" [Broken] link you will see that Lagrange points 2-5 really on the fact that the bodies are in circular motion around the common centre of mass. This dosn't apply in this case. Lagrange point 1 may exist, however since the galaxies are not points or spheres it probably will not be a point be more of an extended region of low potential, rather than a definite trough.

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