New Study Sets Stronger Mass Limit on Ultralight Bosonic Dark Matter

Over 80 years, dark matter has been a great mystery for the researchers. Elusive of direct observation, it has made its existence known only by the gravitational impacts it makes on cosmic structures. Even though there is a lot of indirect evidence of its existence, the real nature of dark matter is still unknown. An important attribute of its particle is mass. While past studies have constrained the mass of fermionic dark matter using quantum principles like Pauli's exclusion principle, bosonic dark matter remained less constrained. In a recent study, scientists have estimated a new lower bound on the mass of ultra-lightweight bosonic dark matter particles.

About the study

According to the study published in Physical Review Letters, 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.

The team of researchers, led by the first author of the study, Tim Zimmermann, a Ph.D. candidate at the Institute of Theoretical Astrophysics, University of Oslo, focused their method 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. By analyzing the internal motions of stars within Leo II—heavily influenced by dark matter—the team derived 5,000 possible dark matter density profiles using a tool called GRAVSPHERE.

They compared these with profiles generated by quantum wave functions of various dark matter particle masses. If the particle is too light, quantum fuzziness spreads it too thinly, preventing it from forming the observed structures. The study concluded that the dark matter particle must have a mass greater than 2.2 × 10⁻²¹ electron volts (eV)—over 100 times more than previous lower estimates.

Impact on dark matter studies

The findings have significant implications for popular ultralight dark matter models, particularly fuzzy dark matter, which typically proposes particles with masses around 10-22 ev.

Looking ahead, the team plans to extend their methodology to mixed dark matter scenarios, where dark matter is composed of particles with different masses.