Abell 2218 Lensing
The picture below of galactic cluster Abell 2218 has been proposed as proof of gravitational lensing due to dark matter. I suggest there is an alternate interpretation.
A brief summary of the picture: stars, galaxies, various segments of bright filament arcs. I noticed there are other images of this cluster on the web that offer more details around the edges with higher resolution (that I refer to below). This article contains the accepted interpretation.
There are diffuse galaxies (near the bottom or at right; perhaps these are ellipticals) and there is an unusual one to the left with the outer ring of stars apparently separated from the core. Some of the small objects are probably galaxies more distant than the rest. Some look 'normal' while others do not in this picture. Perhaps in the future a much higher resolution picture will be taken.
Plasma filaments are known to connect between galaxies to make very large structures. The plasma segments in this picture are apparently due to plasma excitation changing between plasma glow or arc mode (bright) or dark current mode (not bright enough to be seen).
There are so many known configurations of galaxies (some are one of a kind like Hoag's Object) and this picture contains a few.
Hoag's Object is known as a ring galaxy as its shape is a ring of its stars but without an observed core.
the galaxy PGC 1000714 has two rings: an outer ring and an inner ring.
A disc galaxy (like NGC 253) is a galaxy characterized by a disc, a flattened circular volume of stars and it may or may not include a central non-disc-like region (a galactic bulge).
For this picture to be confirmation of gravitational lensing by dark matter the following must be true:
1) The above interpretations (i. e. what you see is correct and not a distortion) are discarded
2) The observations are assumed to be visual distortions of distant objects
3) The theory is dark matter caused the distortions.
4) To confirm a theory there must be a hypothesis to test, to either confirm or deny the hypothesis.
5) the predicted test results have been confirmed.
Unfortunately there are no known predictions to confirm for this scenario.
The necessary prediction would have specified (for the proposed change in space time curvature) a specific amount of dark matter at a specific distance from the light source to the lens object. I assume the proposed dark matter would have a non-symmetric mass distribution for the correct calculation of the observed angular deviation. Unfortunately I have not found such a prediction for dark matter with such details. For now 'some' of it is just 'there' until dark matter can be further defined.
This prediction is not possible given dark matter has no known characteristics, other than it provides an undetectable source for a force attributed to gravity.
When there is no prediction to test for dark matter than how could it be confirmed?
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