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Another way of stating this question: Does the fact that a star system (or comparable concentrated mass) exists in a galaxy affect its long-term evolution, in terms of expansion, contraction, nebulation, etc.?

This question was inspired by a view of the "Umbrella Galaxy" where previous interactions have torn streams of stars far from the galactic disk.

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By star systems, do you mean planetary systems around stars? –  Takku Jul 2 at 16:30
A civilization living in a planet in one of those stars will have certainly an amazing sky view :) –  Joan.bdm Jul 3 at 6:55
@Takku: Not necessarily, but let us say masses of sufficient concentration that they could form a star or small system of stars, but not so massive that they could form a cluster with galaxy-like characteristics (whatever those may be ... separate question?). –  feetwet Jul 3 at 20:38

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The local environment is very important to star formation because it requires material as well as something to perturb the nebula to start collapsing and forming star(s). Therefore, both the type of galaxy as well as the location in the galaxy are very important to creating stars.

However, once a star moves from protostar onto the main sequence, external influences don't much affect its development. This is how we can identify stellar streams because the stars come from a similar population when they are created, but some tidal forces cause them to spread out around the galaxy.

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Can you clarify: Are you just saying that in practice we don't find sufficient concentrations of material outside of galaxies to form star systems? Or rather that local forces are insufficient to start nucleation in an otherwise adequate concentration of matter? Imagine, for example, that a stellar stream strands a small system gravitationally far from any galaxy. Are you saying that without galactic forces to bring the matter back together, or in contact with other matter, then when the system's stars have died/exploded they are unlikely to be able to restart the stellar lifecycle? –  feetwet Jul 30 at 0:48
Interaction is what helps get the adequate concentration. I.e. it's not just the mass that's important, but the density of the region to start the nucleation. Having other gas and dust clouds to interact and increase local densities makes the process more efficient. –  Aaron Aug 16 at 0:19

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