We're getting farther from the Great Attractor (anyone have details on this?)

[Martin]

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/990924a2.html

 

"...is now thought that the Great Attractor is probably a supercluster, with Abell 3627 near its center..."

 

The date on that NASA public outreach page is 1999. Anybody have an update? Additional detail?

 

Wikipedia refers to the concentration around Abell 3627 as "ACO 3627" and says there could be an even more massive concentration ("Shapley") out beyond the G.A., discovered in 2005.

http://en.wikipedia.org/wiki/Great_Attractor

So the G.A. may have been "demoted"

"The survey also confirmed earlier theories that the Milky Way galaxy was in fact being pulled towards a much more massive cluster of galaxies near the Shapley Supercluster which lies beyond the Great Attractor.[3]"

 

Wiki (not always reliable) does cite a source!

http://www.ifa.hawaii.edu/info/press-releases/kocevski-1-06/

And the source in turn cites two 2005 scientific papers:

http://arxiv.org/abs/astro-ph/0510106

http://arxiv.org/abs/astro-ph/0512321

So here is some unresolved controversy and you have to weigh and decide for yourself.

 

The topic of the G.A. came up recently. I recall hearing about G.A. in the 1980s, and an estimate that the Milkyway galaxy, and collectively the Virgo supercluster which we and our little local group of galaxies belong to, are all moving towards the G.A. Not that we are getting closer to it, just that we are moving in that direction.

 

By the early Naughties (bad pun for the 2000s) the microwave background data had come in and it was estimated the speed was roughly 500-600 km/s relative to the Background. (But this did not cause a blueshift, it only meant there was less redshift than otherwise.)

 

That picture may have been revised some, but assume all that is at least approximately right. Then you might intuitively suppose that we are getting CLOSER to the G.A. That given sufficient time we might meet and merge with it. This was conjectured in another thread.

 

But cosmology buffs will realize that this doesn't follow. The G.A. is receding from us, or if you prefer, we are receding from it. The distance is increasing. What astronomers actually measure is a REDSHIFT in the light from the Abell 3627 supercluster. The redshift is just not as large as you'd ordinarily expect for something at that distance.

 

In other words we are not expected ever to meet and merge with the G.A. supercluster, or supersupercluster, however you like to classify it.

 

It would be great to get some recent links about local motions like this. How are they measured, or at least estimated, what kind of inference is used?

Edited January 30, 2010 by Martin