galaxy rotation question

[hoola]

Could the expansion of space affect the star rotations in the outer regions of galaxies? Since lamda has negligent effect on solar system scales, newton prevails. With the outer stars of galaxies being gravitationally bound to the core, and with their orbital distances resisting the increase, could not lamda be converted into a small forward thrust?

Edited September 10, 2016 by hoola

[Mordred]

This question belongs more in the astronomy forum.

 

To answer your question the answer is no. The energy density of lambda is roughly 10^-10 joules/metre^3. Gravity can easily overpower lambda for a considerable distance beyond the last star.

 

In point of detail the cutoff point that defines the outer edge of a galaxy is when the galaxies mass density at a given radius is 100 times the background density. That may seem odd given DM distribution but were dealing with density.

 

Secondly galaxies are gravitationally bound to large scale structures.

Edited September 10, 2016 by Mordred

[hoola]

thank you for the good info....I only ponder that even if gravity overpowers lamda beyond the last star, what happens to the expansion energy that cannot sway those star's orbits? Doesn't that energy have to be expressed in some physical way?

Edited September 10, 2016 by hoola

[Mordred]

Actually lambda isn't accurately described as expansion force. The reason being is all matter and radiation help the universe expand.

Lambda merely helps explain the accelerated rate of expansion. As strange as this sounds even gravity can assist expansion. All according to the conservation laws.

We haven't figured out how lambda fits into the conservation laws as it is the only constant involved out of the three.

 

As the volume increases the mass density of matter and radiation decreases by the ideal gas laws. Lambda does not.

 

Until we understand lambda in that regard we know it assists expansion. However it is not the only cause of expansion.

 

I would recommend reading this article on critical density vs curvature expansion/contraction.

 

http://cosmology101.wikidot.com/universe-geometry

page 2

http://cosmology101.wikidot.com/geometry-flrw-metric/

 

One simplified way to think of expansion.

 

"The competition of all particle species and subsequent fields own self gravity vs it's inherent kinetic energy" its not precisely accurate but it's useful.

 

Every particle type exerts a pressure relationship. This is called an equation of state. Matter with the lowest kinetic energy exerts zero pressure. Radiation exerts the highest pressure influence.

 

https://en.m.wikipedia.org/wiki/Equation_of_state_(cosmology)

Edited September 10, 2016 by Mordred

[hoola]

excellent response, and once again, thank you...

[Mordred]

No problem surprisingly enough Universe expansion is a thermodynamic process. Yes it ties into GR but we incorporate gravity into the thermodynamics so to speak.

 

If you look at the cosmology101 link on my signature you can find several textbook style articles. Mostly published on arxiv.

[Airbrush]

Could the expansion of space affect the star rotations in the outer regions of galaxies?

 

The expansion of space has nothing to do with individual galaxies. It only applies to the separation between superclusters of galaxies. Within our own Virgo supercluster absolutely nothing happens to the galaxies due to the expansion of space. We are all gravitationally bound together forever. Expansion of space is something that takes place far FAR away. Beyond the edge of our supercluster.