Cosmological Redshift distance to where it begins?

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1. Mar 26, 2017

rmpearlman

what is thought to be the closest star whose light visible to us now is/has cosmological redshift?
perhaps the same answer but in case not:
at what LY distance does the prevalent cosmological redshift of distant starlight begin?
TY, r

2. Mar 26, 2017

Staff: Mentor

Typical velocities of galaxies relative to the cosmic microwave background are 400 km/s, dividing that by the Hubble constant gives a typical length of 18 million light years, after that distance cosmological redshift is more important than random motion.
The largest gravitationally bound structures are larger than this. Not every galaxy further apart has follow the Hubble flow nicely.

3. Mar 26, 2017

rmpearlman

TY,
so there would be some cosmic expansion w/in the 18 M LY radius but it is not yet material relative to the normal orbital velocities till that?

4. Mar 27, 2017

Staff: Mentor

Here is an example, 18 Mly = 6 Mpc.
The 400 km/s are a typical value, but it differs a lot between different galaxies.

5. Mar 27, 2017

BenAS

But the force that drives expansion is occurring everywhere, even within galaxies between stars? Just that it's not measurable / important considering the force of gravity?

6. Mar 27, 2017

Staff: Mentor

While there is dark energy, it doesn't lead to an expansion of the galaxies, as they are gravitationally bound. If we could measure the orbits and all masses with infinite precision we could see the effect on the orbits, but in reality we cannot, it is completely negligible within galaxies.