Galactic Pairs

[Skaffen]

I was watching a Susskind lecture where he pointed out that all but the nearest Galaxy to ours (Andromeda?) is moving away from us - It was a lecture on Special Relativity, which is the main context behind my question.

 

Do Galaxies come in pairs?

Is Andromeda of a similar magnitude to the Milky Way?

 

Any help much appreciated.

Rgds, Skaff.

[Sisyphus]

Galaxies do not come in pairs. Andromeda is of a similar magnitude as the Milky Way. There is also one other spiral galaxy in our local group, and about 30 smaller ones.

 

The reason all but the closest are getting farther away from us is because of cosmic expansion - the "amount of space" in the universe is increasing. At large distances, this effect is greater than any local motion towards us.

[Skaffen]

Galaxies do not come in pairs. Andromeda is of a similar magnitude as the Milky Way. There is also one other spiral galaxy in our local group, and about 30 smaller ones.

 

The reason all but the closest are getting farther away from us is because of cosmic expansion - the "amount of space" in the universe is increasing. At large distances, this effect is greater than any local motion towards us.

 

I don't like the term 'space is increasing', seems to defy conservation. 'Reconfigured' perhaps? There are after all forces we are only just beginning to encounter, never mind understand. (ie Dark Energy)

 

Further reading led me to the 'Holmberg Effect', which does strongly suggest a correlation (pairing/grouping of Galaxies)

[Sisyphus]

Conservation of what?

 

What is it that you read about the Holmberg Effect that led you to believe that galaxies "come in pairs?"

[Skaffen]

Conservation of what?

 

What is it that you read about the Holmberg Effect that led you to believe that galaxies "come in pairs?"

 

http://www.astro.uu.se/history/holmberg.html

 

 

- "A study of double and multiple galaxies" (1937) he showed that galaxies often appear in groups and pairs and he also realized that it would be possible, using statistics, to determine the masses of pairs of galaxies knowing the radial velocities of the components and this method has been very important in extragalactic research. The observations also resulted in the discovery that satellite galaxies often move in certain orbits, the "Holmberg effect".

 

http://www.astro.uu....y/holmberg.html

 

 

- "A study of double and multiple galaxies" (1937) he showed that galaxies often appear in groups and pairs and he also realized that it would be possible, using statistics, to determine the masses of pairs of galaxies knowing the radial velocities of the components and this method has been very important in extragalactic research. The observations also resulted in the discovery that satellite galaxies often move in certain orbits, the "Holmberg effect".

 

-"Conservation of what?"-

Of the amount of space. You can stretch an elastic band, it doesn't infer there is more. Opening an umbrella doesn't increase anything because I can conserve by closing it again, it is a reconfiguration. The principle of conservation is axiomatic, when you talk in terms of more space it is due to oversimplification.

[Sisyphus]

That doesn't say that galaxies come in pairs. It says that they often group up, which they do. There is nothing special about the number 2 in particular.

[Skaffen]

That doesn't say that galaxies come in pairs. It says that they often group up, which they do. There is nothing special about the number 2 in particular.

 

I know it doesn't postulate all galaxies come in pairs - that's what I'm trying to find out. It says they often do based on direct observation, which is a limited set. Susskind says all but 1 is moving away from ours - this suggests IMO our galaxy is paired. The Holmberg Effect is a relationship between pairs, considering he was using old tech I was hoping to gain a contemporary view. Preferably building in Dark Energy and the implications it may have for eventual equilibrium.

[Sisyphus]

As I said, it's cosmic expansion that is the reason they're all moving away. Only very close galaxies would even have the chance to be moving towards us.

 

Here is an image of the galaxies in our immediate vicinity:

 

[Skaffen]

Thanks Sisyphus, cool diagram

 

Seems from that diagram that pairing occurs along the Galactic plane . It is obvervable that Galaxies are related along 'superstrings' as measured by the COBE satellite as an aspect of the Universe 'expanding'. It is the nature of this relationship between Galaxies that prompts the question.