Hidden mass in galaxies

The mass distribution in the universe is studied. The density of matter in the universe is nearly that of galaxies, i.e. one and a half orders of magnitude lower than the critical cosmological density, which is 5.10-30 g/cm3. It is known that the dynamical masses of galaxies differ strongly from the photometric masses. This discrepancy is common to all clusters. On the whole for clusters the mass-brightness ratio is very much higher than for the galaxies contained in them. From the study and modelling of galaxies the authors propose a corona-subsystem in galaxies, which is not visible in the optical region and which causes by its gravitational attraction the differences between the dynamical and photometric mass distributions. With these hidden masses of the coronae the average density of the universe is considerably higher, reaching some 20% of the critical density. From the analysis of radio frequency, optical, u.v. and X-ray radiation of galaxy clusters it is concluded that the coronae in the galaxies consist of compact objects, possibly like stars, planets or nuclei of comets. These objects are, however, not similar to the ordinary stars which can be seen in the galaxies. These objects must have small masses (less than 0.1 sun masses) because of the large total mass and the very weak visible light. Up to now it is not clear how these objects can be formed at the very low densities of the corona (10-25g/cm3 and less) because it is known from actual data that the star-forming process starts only at densities of 10-24g/cm3 and more. The nature of the hidden mass and its role in the formation and evolution of galaxies is one of the most important and actual problems of astrophysics