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What do 28 gravitational lenses reveal about dark matter's true nature?

D. Gilman, A. M. Nierenberg, T. Treu, K. N. Abazajian, T. Anguita, V. N. Bennert, A. J. Benson, S. Birrer, S. G. Djorgovski, X. Du, C. Gannon, S. F. Hoenig, R. E. Keeley, A. Kusenko, H. R. Larsson, M. Malkan, T. Morishita, V. Motta, L. A. Moustakas, P. Mozumdar, H. Paugnat, W. Sheu, D. Sluse, D. Stern, M. Stiavelli, D. Williams, K. C. Wong

June 3, 2026

Astronomers used 28 strong gravitational lenses observed by JWST to measure tiny dark matter clumps around distant galaxies. By precisely mapping how light bends around these clumps, they constrained how freely dark matter particles can move through space—a signature of the particle's mass. The result strongly supports cold dark matter theory and excludes alternative lightweight particles as the universe's dominant matter.
Published as The free-streaming length of dark matter from JWST observations of 28 strong gravitational lenses arXiv:2606.05277
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