Galaxies do not adhere to Kepler's laws, which are applicable only to two-body systems. Instead, galactic behavior is modeled using Newton's laws, with general relativistic corrections being negligible. The discussion emphasizes the need to understand dark matter and explore Modified Newtonian Dynamics (MOND) as a potential framework for explaining galactic motion. It is concluded that while MOND is a significant model, it is not the sole theory available for understanding galaxy dynamics.
PREREQUISITESAstronomers, astrophysicists, and students of physics interested in galaxy dynamics and the underlying principles of motion in celestial systems.
They don't follow Kepler's laws. Those only apply to two masses.Martyn Arthur said:Is it a big assumption that Galaxies should follow Kepler's third law
With the caveat that you mean Newton's laws not Kepler's the answer is:Martyn Arthur said:Is the small tet of the behaviour of the Solar System not too small an example to make such a substantial assumption?
Technically they apply to problems of central motion in a Kepler potential (proportional to 1/r). The second law applies more generally to any central potential as it is related to conservation of angular momentum. However, the first and third laws are contingent on the problem actually being a Kepler central potential.Ibix said:They don't follow Kepler's laws. Those only apply to two masses.
There is more than one modified theory. MOND is not the only game in town and is at best a "toy-model".Ibix said:They don't follow Kepler's laws. Those only apply to two masses.
They are modelled as following Newton's laws (GR corrections are too small to worry about).
With the caveat that you mean Newton's laws not Kepler's the answer is:
1 - no, galactic behaviour is purely Newtonian, we just need to work out what dark matter is.
2 - sort of, we need to include general relativistic corrections to a Newtonian model.
3 - yes, all we need to do is work out how the modified theory, Modified Newtonian Dynamics (MOND), works.
Take your pick which is the correct one...