Dark matter accounts for approximately 85% of the matter in the Universe. However, dark matter is famously elusive and can not be directly experienced. Instead, its presence is deduced through its gravitational pull on the visible matter in space.
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Now, observations of several massive galaxy clusters by NASA's Hubble Space Telescope and the European Southern Observatory's Very Large Telescope (VLT) in Chile have revealed a missing mysterious ingredient to current presiding dark matter theories. Astronomers have discovered that small-scale concentrations of dark matter in clusters produce measurements of how gravity distorts space, also called gravitational lensing effects, that are 10 times stronger than previously expected.
"Galaxy clusters are ideal laboratories to understand if computer simulations of the universe reliably reproduce what we can infer about dark matter and its interplay with the luminous matter," said Massimo Meneghetti of the National Institute for Astrophysics (INAF) Observatory of Astrophysics and Space Science of Bologna in Italy, the study's lead author.
"We have done a lot of careful testing in comparing the simulations and data in this study, and our finding of the mismatch persists," Meneghetti continued. "One possible origin for this discrepancy is that we may be missing some key physics in the simulations."
"There's a feature of the real universe that we are simply not capturing in our current theoretical models. This could signal a gap in our current understanding of the nature of dark matter and its properties, as these exquisite data have permitted us to probe the detailed distribution of dark matter on the smallest scales," added Priyamvada Natarajan of Yale University in New Haven, Connecticut, one of the senior theorists on the team.
Hubble's images, combined with spectra from the VLT, helped the team produce an accurate, high-fidelity dark-matter map that identified dozens of background galaxies. Better yet, by calculating the lensing distortions, the researchers could figure out the amount and distribution of dark matter. The team's paper is published in the journal Science.