The Universe is composed of 81% dark matter, different from the ordinary visible matter formed by atoms.

Invisible, dark matter mainly manifests through the action of gravity; it is one of the essential components of galaxies.

The proportion of dark matter in the total mass of the galaxies varies according to their sizes: 95% for large diluted galaxies (spiral, elliptical and others) up to 99.99% for compact dwarf galaxies.

In such proportions, dark matter and gravity play a decisive role in the formation and structure of galaxies.

Using a theory involving these two components, a european team of scientists, including a scientist from the Observatory of Paris, managed to reproduce the observed properties of galaxies, namely their circular velocities, their density distributions and the relationship between their masses, sizes and velocities.

Warm dark matter

This new theoretical approach is based on the supposed existence of the dark matter called "warm", as opposed to the "cold" dark matter. The "warm" dark matter is composed of particles with mass in the scale of thousand electron volts (eV or keV, equivalent to 10-33 kg, an electron has a mass of 511 keV). In the"cold" dark matter, the particles are much heavier and slower.

The work is based on the microscopic properties of particles of warm dark matter, that is to say, their quantum properties (such as the spin and the statistics associated with the particles): a repulsive pressure is generated, acting against the attractive pressure of gravity.

For this work, ten different independent data sets of galaxies have been used, each set with galaxy masses ranging from 5 × 109 to 5 × 1011 solar masses.

The obtained circular velocities of galaxies (rotation curves) and density distributions are consistent with those observed. And remarkable feature: the normalized theoretical rotation curves and density profiles are universal: they are the same for all the galaxies of different types, sizes and masses.

The compact dwarf galaxies are thus close to the high dense gas (Fermi gas or gas of degenerate fermions), while larger and intermediate galaxies (spiral, elliptical and others) are close to the classical diluted gas (known as Boltzmann ).

These studies also confirm the few of correction could cause the baryonic matter (the "ordinary" matter), result which is consistent with the small fraction (up 5%) it represents in galaxies.

This novel theoretical approach to the structure of galaxies puts together gravitation and quantum properties of dark matter. It has its counterpart in the statistical approach used for atoms (known under the name of "Thomas-Fermi"), with gravitation playing the role of the electric potential; in other words, "Newton, Fermi and Dirac meets together in galaxies through dark matter," points out Norma Sanchez, one of the main authors of the study.

Reference

• "Observational rotation curves and density profiles versus the Thomas-Fermi galaxy structure theory", H. J. de Vega; P. Salucci; N. G. Sanchez Monthly Notices of the Royal Astronomical Society 442 (2): 2717-2727 (2014)

Last update on 21 December 2021