Talk:Great Attractor

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[edit] What is the Great Attractor?

So what is this gravity anonymous? A blackhole? (--61.64.74.148 (talk • contribs), 10 June 2004)

If I understand this correctly, it's too large to be a hypermass. (--Stargoat, 14 July 2004)

What is a "hypermass", and why can't this be one? (--66.156.239.23 (talk • contribs), 5 August 2004)

The most down to earth theory would be that the Great Attractor is a dense collection of galaxies. We can't see it, at least not with current technology, like we can with the Virgo cluster, because it is in the galactic plane, so we need to look through all of the "light pollution" from the stars in the Milky Way. Salleman (5 June 2005)

"Hypermass" is another term for black hole, no longer in common usage (though it crops up occasionally).--Christopher Thomas 01:12, 21 Jun 2005 (UTC)

Could it be a complex spacetime fold,which magnifies gravity?

It could be, but why would we even begin to think about such complex and improbable things like that when regular old matter seems to do the trick? --Gwern (contribs) 20:46 3 December 2006 (GMT)

[edit] Distances

--Just curious...the Virgo supercluster article states that this supercluster is 200 mil LYs in diameter, and this article claims the Great Attractor is (recently measured) 250 mil LYs away from us and is at the center of the supercluster. Can anyone explain this discrepancy? --Jleon 15:16, 11 January 2006 (UTC)

If I understand correctly, the discrepancy is due to the fact that our measurements of distance at those ranges aren't very accurate, though accuracy is improving. --Christopher Thomas 17:28, 23 February 2006 (UTC)

[edit] Moving away from each other

Is it true that the galaxies in the local supercluster are all receding from each other? I'm hazy on whether or not the supercluster is gravitationally bound (which would mean they weren't receding). --Christopher Thomas 17:28, 23 February 2006 (UTC)

Technically, That's not possible.--Mac Lover ^Talk 17:06, 10 August 2006 (UTC)

Clarify, please (starting with what you're calling impossible, then why). --Christopher Thomas 22:16, 10 August 2006 (UTC)

If you imagine 2 ants on opposite of a balloon as its blown up. Both are walking towards the end. Although they are walking to the same spot the are getting further appart as the balloon expands. So yes, it can be gravitationally bound while still moving apart. As it gets further apart though some parts will no longer be bound, as gravitational affect decrease with distance. Thats enough abstract thought for me for tonight. --LiamE 00:03, 11 August 2006 (UTC)

I wouldn't consider a system like that to be gravitationally bound in an expanding universe, precisely because the components have net motion away from each other, even if local motion is in the direction of the center of the system. For an example of a system I'd call "bound", consider a hydrogen atom, or the Earth in orbit about the Sun). In both of these examples, the net effect of cosmic expansion is to add a radial acceleration term when you set up the equations of the system, causing the stable orbit radius to be (very) slightly shorter than it would be in the absence of expansion, allowing increased attractive forces to produce an effect that exactly balances the acceleration due to metric expansion of space. Before anyone objects, note that I'm not claiming that metric expansion itself applies a force - instead, I'm treating it as causing _acceleration_ when the system equations are set up using proper distance instead of comoving distance. --Christopher Thomas 00:41, 11 August 2006 (UTC)