Insights into Dark Matter's 'Coldness' Open New Cosmic Frontiers

Cold Dark Matter Viel

A new study conducted by an international collaboration that includes the University of Cambridge and SISSA, reveals vital clues about the 'coldness' of dark matter, the mysterious component making up 80% of all matter in the universe, showing a deep connection between dark matter and the formation of galaxies in the early Universe.

The new findings, published in Physical Review D, suggest that the abundance of small galaxies in the cosmos aligns with the presence of 'cold' dark matter, while scenarios involving 'warm' dark matter lead to a smoother cosmic web, devoid of smaller galactic structures. 

Through meticulous numerical simulations, researchers explored various scenarios, from the dense, slow-moving particles of 'cold' dark matter to the lighter, faster particles of 'warm' dark matter. These scenarios were compared with observations of extremely distant quasar spectra, observing the universe when it was just 1 billion years old thanks to the latest generation of telescopes.

“Arriving at a crucial conclusion in this study we have challenged the notion that dark matter is composed of exceptionally light particles,” said Vid Irsic, first author of the paper and Senior Kavli Fellow at Cavendish Laboratory, University of Cambridge.

“By scrutinising quasar spectra from the Universe's infancy, we have excluded certain particle masses (thousands of times the mass of an electron or lower), narrowing down the possibilities for dark matter's composition.”

“Through the combination of new data and better simulations, we were able to increase our confidence in ruling out light and fast dark matter species as the primary component of the elusive dark sector (dark matter and dark energy) of the Universe,” said second author of the paper Matteo Viel from SISSA, Italy.

The findings not only deepen our understanding of dark matter but also provide further clues for solving longstanding cosmic mysteries. By ruling out certain dark matter scenarios, scientists can now focus their efforts on more promising avenues.

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Paper: Iršič V. et al. 'Unveiling dark matter free streaming at the smallest scales with the high redshift Lyman-alpha forest', Physical Review D, Feb. 2024; DOI: 10.1103/PhysRevD.109.043511