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The term "Hubble flow" refers to the homologous expansion of space and the resulting recession of all galaxies from each other (if they're not close enough to be gravitationally bound). This effect causes the "cosmological redshift", i.e. the redshift that light from distant galaxies attain as it travels through space. In addition to this ...

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Not quite. Gravitational redshift is proportional to $M/R$, where $M$ is the mass interior to a radius $R$. However density $\rho$ is proportional to $M/R^3$. So gravitational redshift does not depend directly on density. If you are considering radiation emitted from the surface of an object then the redshift is proportional to either $\rho R^2$ or \$\rho^{1/...

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Redshift is not related to the time it takes to travel from the source to the viewer, not to the distance from the source to the viewer. But light is red-shifted by travelling out of a gravitational well. One way to see this is to consider the equivalence principle: A person at the front of an accelerating spacecraft would see light shone from the back to ...

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