Hydrodynamics of large scale structure formation

The concordance model

The Lambda-CDM (Cosmological constant + Cold Dark Matter) or concordance model is known to describe the present cosmological data very well. It assumes 4-5% of matter in baryons, 20-25% as dark matter and 70-75% as dark energy. The latter explains the dimming of supernova events.
But this theory is also known to involve various further assumptions and, worse, to fail in a growing number of details. Despite many searches the presumed cold dark matter particle has not been found, which is becoming worrying. Very recently there appeared in Nature two papers on the observation of a Gamma Ray Burst of 630 million years after the Big Bang (13.1 billion years ago). Since this approaches the ``dark age'' till 400 million years after the Big Bang, where the concordance model predicts the absence of stars, it is legitimate to investigate scenarios without dark age.
There are many more questions about the concordance model, let us mention some. An old question is why so few clusters are formed by the Jeans mechanism, only 149 globular star clusters are observed in the Galaxy, while millions are possible. Other issues relate to observed correlations in galaxy structure, that do not reflect hierarchical clustering; galaxies formed fairly early, up to one billion years after the Big Bang; and dwarf satellites that swarm our Galaxy just like its stars and that have a large proportion of dark matter.


Galactic Dark matter: the gravitational hydrodynamics picture

Dark matter is commonly attributed to MACHOs (massive objects like planets), WIMPs (elementary particles), axions, etc. Gravitational hydrodynamics explains that baryonic MACHOs form the galactic dark matter. Indeed, of the 4-5% baryonic matter, only about 0.5% is visible in stars and 2-2.5% in X-ray gas, so the remainder may well be locked up in MACHOs.

Hydrodynamics of the protoplasma before and after decoupling (transformation of the plasma into neutral gas) proposes a new picture of structure formation. It is top-down, rather than bottom-up. Its first main point is that the photon-viscosity of the plasma is so important, that structure formation of baryons can start without help of CDM. Before decoupling (transformation of the plasma into neutral gas) the viscosity creates an instability that makes the plasma fragment into proto-galaxy-clusters and proto-voids; these have now developed into existing galaxy clusters and voids.

After decoupling the Jeans mechanism fragments all the gas into Jeans clusters of roughly 40.000 solar masses, some of which became the observed globular clusters. But most of them became dark and constitute a dark halo of ca. 100 million Jeans clusters around each galaxy. Their isothermal distribution explains the flattening of galaxy rotation curves and the Tully Fischer relation, i. e., galaxy-luminosity proportional to (rotation velocity)^4.

The Jeans clusters are themselves also fragmented -- again due to viscosity, but this time in the gas after the decoupling -- in milli brown dwarfs or earth mass. The first stars occur by merging of still hot milli brown dwarfs, without dark period. They are ordinary stars, not the presumed 1000 solar mass Population III stars of the concordance model.
Most of the milli brown dwarfs are frozen now, but can be reheated, e. g. in galaxy merging and planetary nebulae. Thousands of milli brown dwarfs have been observed in microlensing and, reheated by the central white dwarf, tens of thousands in planetary nebulae.

In galaxy merging, various already present, dark Jeans clusters are heated; this happens along the paths where the galaxies enter each others dark matter cloud. Tidal forces reheat the milli brown dwarfs, they expand, coalescence and form new stars, which turns those Jeans clusters into the young globular clusters, as observed along the respective paths of these galaxy mergers.
Cluster dark matter (dark matter in clusters of galaxies) is described in the section on neutrino hot dark matter.

[C46] Theo M. Nieuwenhuizen, Carl H. Gibson and Rudy E. Schild
Gravitational hydrodynamics vs observations of voids, Jeans clusters and MACHO dark matter
arXiv:1003.0453 , (3 pp). Proceedings Marcel Grossmann XII, Eds. Thibault Damour, Robert T Jantzen and Remo Ruffini, World Scientific, Singapore, 2010