3 ms·

Considering the three body problem and extrapolating I would expect star orbits in a galaxy to be completely chaotic on long time scales?

• deleted 2y ago
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• neutronicus 2y ago
  A galaxy is a pretty degenerate instance of the n-body problem, though. A system of one or two giant bodies orbited by a collection of tiny ones. Each tiny one spends most of its time in a very weakly-perturbed two-body problem, quasi-stably orbiting the giant one(s) with tiny deviations caused by all the other ones. So you have to do some statistics to see how often an assumed distribution of quasi-stable orbits results in the tiny bodies approaching each other closely enough to kick one another into meaningfully different orbits of the giant ones. This gives you a better idea of how long is "long" and how it compares to the age of the universe
• privong 2y ago
  > Considering the three body problem and extrapolating I would expect star orbits in a galaxy to be completely chaotic on long time scales? That's more or less captured by the loss cone calculation. On a very "long time scale" the loss cone will probably be occasionally replenished by stars coming in from scattering on larger scales, but the timescale for this to become significant for galaxies is substantially longer than the age of galaxies (and also longer than the Hubble time, which is the ~age of the Universe). So, at least from this back of the envelope calculation, that doesn't solve the final parsec problem. See, e.g., https://www.astro.umd.edu/~richard/ASTRO620/Dynamics_Lec3.pdf https://www.astro.umd.edu/~richard/ASTRO620/Dynamics_Lec3.pd...
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