Why should the Bullet Cluster focus light?

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    Bullet Focus Light
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Discussion Overview

The discussion centers around the gravitational lensing effects observed in the Bullet Cluster, particularly questioning why the gas mass between the two galaxy clusters does not focus light despite its significant mass. Participants explore the nature of gravitational lensing, the role of dark matter, and the implications for modified gravity theories.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants question the assumption that the gas mass in the Bullet Cluster should focus light, suggesting that its shape could affect lensing behavior.
  • Others argue that gravitational lensing does not require coherence in the same way optical lenses do, pointing out that multiple images can arise from different paths light takes around a mass.
  • A participant emphasizes that the total mass of the cluster, rather than its distribution, is what matters for gravitational lensing effects like Einstein Rings.
  • There is a contention regarding the necessity of coherent curvature for light to be magnified, with some asserting that the lensing effect occurs around the cluster rather than through it.
  • One participant highlights the significance of the Bullet Cluster in demonstrating flaws in modified gravity theories (MOND) by showing that dark matter can be inferred through gravitational lensing.
  • Another participant expresses uncertainty about the arguments presented, suggesting that proponents of MOND claim their theories can bend light similarly to dark matter.

Areas of Agreement / Disagreement

Participants express differing views on the nature of gravitational lensing and the role of mass distribution. There is no consensus on whether the gas mass should focus light or how it relates to the presence of dark matter.

Contextual Notes

Participants note the complexity of gravitational lensing and the assumptions involved in interpreting the Bullet Cluster's observations. There are unresolved questions regarding the relationship between mass distribution and lensing effects.

  • #31
Earnest Guest said:
From your comments, you also don't understand the difference between strong lensing and weak lensing. I suggest you go back and review the materials before trying to act as an 'advisor' on this subject again. There is simply no foundation for being able to simplify a weak lensing problem as a point source. You must perform a statistical analysis of all the stars in a region before you can draw a contour map. There's some good material on the Wiki pages about it.
https://en.wikipedia.org/wiki/Weak_gravitational_lensing
Earnest Guest said:
I'm afraid you just haven't been following the conversation. In addition, I don't think you have a grasp of the concepts here. The Bullet Cluster doesn't have enough mass to create any strong lensing effects. The only effects are 'weak' lensing effects which can only be seen in a statistical blip in the shape of the stars inside the projected radius of the cluster.

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  • #32
marcus said:
?
Exactly
 
  • #33
The weak lensing effect extends out beyond the projected radius of the cluster which is causing the lensing.

And it is typically measured from the distortion of the shapes of galaxies (not individual stars) which are out beyond the cluster causing the lensing.
 
  • #34
phinds said:
Just as an aside, you have STILL never acknowledged your mistake in thinking that convexity/concavity has something to do with gravitational lensing and that there is a similarity with optical lensing. Do you still believe that it is true?
Take two black holes. Place them relatively close together. Now look at a distant SNe Ia that lies directly between the two black holes. Will this supernova appear to be magnified or de-magnified?
 
  • #35
This may be a case of "don't feed the argument". We've had plenty of calm peaceful friendly discussion of weak lensing (e.g. as used to map concentration of DM mass) here at PF since, as I recall, 2005. We don't need vituperation about who said what and who was wrong etc etc. It doesn't add any useful understanding. AFAICS. That is just my private opinion---I'm not a mentor (they do the moderating).
I'd give everybody a pass and lock the thread, if it were up to me.
 
  • #36
Closed pending moderation.

Edit. I think we will leave it closed. Everyone has voiced their position.
 
Last edited:

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