The dark matter of the Abell 1689 Galaxy Cluster is modeled by thermal, non-relativistic gravitating fermions and its galaxies and X-ray gas by isothermal distributions. A fit yields a mass of h₇₀^½(12/)^1/4 1.445(30) eV. A dark-matter fraction Ω_ν=h₇₀^-3/20.1893(39) occurs for = 12 degrees of freedom, i.e., for 3 families of left- plus right-handed neutrinos with masses 2^3/4G_F^1/2m_e². Given a temperature of 0.045 K and a de Broglie length of 0.20 mm, they establish a quantum structure of several million light years across, the largest known in the Universe. The virial α-particle temperature of 9.9±1.1 keV/k_B coincides with the average one of X-rays. The results are compatible with neutrino genesis, nucleosynthesis and free streaming. The neutrinos condense on the cluster at redshift z~28, thereby causing reionization of the intracluster gas without assistance of heavy stars. The baryons are poor tracers of the dark-matter density.

14.60.St Non-standard-model neutrinos, right-handed neutrinos, etc.

95.35.+d Dark matter (stellar, interstellar, galactic, and cosmological)

98.65.-r Galaxy groups, clusters, and superclusters; large scale structure of the Universe

Particle physics and field theory

Astrophysics and astroparticles

Issue 5 (June 2009)

Received 13 May 2009 , accepted for publication 18 May 2009

Published 29 May 2009