Our Local Group's Microwave Background Radiation dipole

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Discussion Overview

The discussion centers on the orientation of the Local Group's dipole for Microwave Background Radiation (CMB) and its relationship to the gravitational dynamics of superclusters, particularly the Virgo and Hydra-Centaurus superclusters, as well as the Great Attractor. Participants explore the implications of these dynamics on the observed CMB dipole direction.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants question why the Local Group's CMB dipole is not aligned with the center of mass of the Local Supercluster, suggesting that clusters should be infalling towards their supercluster's gravitational well.
  • Others propose that the observed dipole is influenced by a greater flow towards the Great Attractor, which is suggested to be a concentration of superclusters, with the motion towards it being significantly faster than the Virgocentric flow.
  • One participant introduces the idea that the Local Group could be accelerating towards the center of the Virgo cluster while orbiting around it, noting that their motion relative to the CMB is orthogonal to the Virgo cluster's center.
  • Another participant references discrepancies in the observed CMB dipole direction relative to the positions of various superclusters, raising questions about potential contradictions in the data.
  • Some participants provide external references and resources to support their claims regarding the dynamics of the Hydra-Centaurus supercluster and its relation to the Great Attractor.
  • One participant challenges the correctness of a previous claim by referencing a textbook that discusses the gravitational influences on the Hydra-Centaurus supercluster.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the CMB dipole and the gravitational dynamics of superclusters. There is no consensus on the reasons for the observed dipole orientation, and multiple competing explanations are presented.

Contextual Notes

Participants highlight potential contradictions in the observed data regarding the CMB dipole and the positions of superclusters, indicating that further clarification on these points may be necessary.

zankaon
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Why isn't our Local Group's dipole for Microwave Background Radiation pointed towards the center of mass for our Local Supercluster? Clusters are suppose to be just infalling towards gravitational well of it's supercluster. http://en.wikipedia.org/wiki/Cosmic_microwave_background"
See anisotropy velocity relative to CMB section.
 
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Because there is a greater flow than this virgocentric flow. It takes the Virgo supercluster and the Hydra-Centaurus supercluster towards the "Great Attractor". This is probably a concentration of more superclusters having the Norma cluster at its center. The virgocentric flow takes place within this "river" of matter and galaxies and is about 200 km/s. However, the motion towards the Great Attractor is about 600 km/s, and is therefore one that is more visible in the CMB dipole.
 
We could be accelerating towards the centre of the Virgo cluster, but orbiting around it.

Our motion relative to the CMB (allowing for our motion around the galactic centre) is roughly orthogonal to the direction of the centre of the Virgo cluster, just like the direction of the Earth's motion is more or less orthogonal to the direction of the Sun.

Garth
 
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zankaon said:
Why isn't our Local Group's dipole for Microwave Background Radiation pointed towards the center of mass for our Local Supercluster? Clusters are suppose to be just infalling towards gravitational well of it's supercluster. http://en.wikipedia.org/wiki/Cosmic_microwave_background"
See anisotropy velocity relative to CMB section.

Web site: http://en.wikipedia.org/wiki/Great_Attractor"
has a nice 2MASS etc. infrared sky. On large magnification, our Local Group's dipole in relation to CMB frame of reference is in direction of Hydra/Centaurus s.c.s at redshift Z .016 and .02. This is somewhat off from Shapely concentration at Z .048. This differs markedly from a Virgocentric infall. The image refers also to Norma s.c. Z .016 and nearby supposed G.A. which differs markedly from CMB dipole - contradiction? Also the text refers to Norma being near to Hydra/Centaurus - another contradiction?
 
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I don't think this is correct. Carroll & Ostlie in "An Introduction to Modern Astrophysics" mention that the Hydra-Centaurus supercluster is also being pulled by the Great Attactor. Same you can read in this page here: http://www.solstation.com/x-objects/greatatt.htm. In wikipedia you can read that it is currently assumed to have the Norma cluster in its center.
 

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