= Gravitational lensing by a galaxy cluster
The projected gravitational field of a <galaxy cluster> bends light from background sources, producing strong-lensing arcs and multiple images near critical curves, and weak coherent shape distortions farther out. Joint analysis probes total projected <mass> rather than just luminous matter. Source <distances>, shape calibration, line-of-sight structure and degeneracies in the <mass> model limit inference; lensing alone does not identify a dark-matter particle.
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