Researchers establish fundamental limit on how light bosonic dark matter can be

Summary

by Tejasri Gururaj , Phys.org Visualization of a dark matter wave function density reconstructed from Leo II observations. Credit: Physical Review Letters (2025). DOI: 10.1103/PhysRevLett.134.151001 In a new study published in Physical Review Letters, scientists have estimated a new lower bound on the mass of ultra-lightweight bosonic dark matter particles. Purported to make up about 85% of the matter content in the universe, dark matter has eluded direct observation. Its existence is only inferred by its gravitational effects on cosmic structures. Because of this, scientists have been unable to identify the nature of dark matter and, therefore, its mass. According to our current model of quantum mechanics, all fundamental particles must be either fermions or bosons. Previous work has successfully established the lower bound on dark matter's mass (if it is fermionic) using Pauli's exclusion principle. Pauli's exclusion principle prevents two fermions (electrons, protons, neutrons) from occupying the same quantum state simultaneously. However, this doesn't apply to bosons (photons, gluons, Higgs particles). Phys.org spoke to the first author of the study, Tim Zimmermann, a Ph.D. candidate at the Institute of Theoretical Astrophysics, University of Oslo. Zimmermann said, "Through the lens of astrophysics, a productive way to constrain the properties of dark matter is to extract from observations what it is not. In this work, we establish a new fundamental limit on the mass of the dark matter particle, assuming it falls into the ultralight boson category." According to their study, the mass of ultralight bosonic dark matter must be more than 2 × 10-21 electron volts (eV), 100 times more than previous estimates using Heisenberg's uncertainty principle. Kinematical observations of Leo II The team's method focuses on the data of Leo II, the Milky Way's satellite galaxy. It is a dwarf galaxy 1,000 times smaller than the Milky Way. "What we need is a single snapshot of how ...