Gravitational hydrodynamics of large-scale structure formation

The gravitational hydrodynamics of the primordial plasma with neutrino hot dark matter is considered as a challenge to the bottom-up cold-dark-matter paradigm. Viscosity and turbulence induce a top-down fragmentation scenario before and at decoupling. The first step is the creation of voids in the plasma, which expand to 37Mpc on the average now. The remaining matter clumps turn into galaxy clusters. At decoupling galaxies and Jeans clusters arise; the latter constitute the galactic dark-matter halos and consist themselves of earth mass milli brown dwarfs. Frozen milli brown dwarfs are observed in microlensing and white-dwarf-heated ones in planetary nebulae. The approach explains the Tully-Fisher and Faber-Jackson relations, and cosmic microwave background temperature fluctuations of sub-milli-kelvins. Copyright c © EPLA, 2009 Introduction. – Structure formation in the Universe starts in the plasma of protons, electrons, He atoms and neutrinos, that exists up to some 400000 yr after the Big Bang, the time of decoupling (dc) of photons from matter (last scattering (L) or recombination). Then the plasma transforms to a neutral gas of H and 24% by weight He, with the neutrinos remaining free streaming. As this occurs at about four thousand degrees kelvin, a moderate plasma temperature, we shall seek an explanation in terms of plasma physics and gravitational hydrodynamics alone. This embodies a return to the top-down scenario of largescale structure formation. Currently it is assumed that cold dark matter (CDM) also exists and, clustered before decoupling, has set seeds for baryon condensation. The so-called the concordance or ΛCDM model involves also a cosmological constant or dark energy. It describes a hierarchical bottom-up approach to structure formation, stars first, then galaxies, clusters, and, finally, voids. But observations of dense clumps of ancient small stars in old globular clusters (OGCs) in all galaxies contradict the ΛCDM predictions that star formation should begin only after about 300 million years of dark ages and (a)E-mail: [email protected] (b)E-mail: [email protected] (c)E-mail: [email protected] that the first stars should be 100–1000M populationIII superstars. OGCs do not spin rapidly so they cannot be condensations, and their small stars imply gentle flows inconsistent with superstars. Other difficulties are posed by empty supervoids with size up to 300Mpc reported from radio telescope measurements [1], dwarf galaxies with a lot of dark matter [2] and a preferred axis of evil spin direction (AE) that appears at scales extending to 1.5Gpc, a tenth of the horizon scale [3]. Nearly every month new observations arise that pose further challenges to the ΛCDMparadigm: Correlations in galaxy structures [4]; absence of baryon acoustic oscillations in galaxy-galaxy correlations [5]; galaxies formed already when the universe was 4–5 billion years old [6] or even 1 billion [7]; dwarf satellites that swarm our own galaxy just like its stars [8]. The recent conclusion by one of us that dark-matter particles must have mass of a few eV and probably are 1.5 eV neutrinos [9], means that dark matter is hot (HDM), urging once more for an explanation of structure formation from baryons alone, without a cold-dark-matter trigger. We shall discuss such baryonic clustering due to a viscous instability in the plasma, overlooked by the currently popular linear models of structure formation. CDM is assumed not to exist, while HDM, though, next to inflation, important to maintain the homogeneity of the plasma, has no role in the structure formation.