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Register a new userAn alternative approach to the galactic dark matter problem
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We discuss scenarios in which the galactic dark matter in spiral galaxies is described by a long range coherent field which settles in a stationary configuration that might account for the features of the galactic rotation curves. The simplest possibility is to consider scalar fields, so we discuss in particular, two mechanisms that would account for the settlement of the scalar field in a non-trivial configuration in the absence of a direct coupling of the field with ordinary matter: topological defects, and spontaneous scalarization.
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In this work, a generalization of the Mazur-Mottola gravastar model is explored, by considering a matching of an interior solution governed by the dark energy equation of state, $omegaequiv p/ rho<-1/3$, to an exterior Schwarzschild vacuum solution at a junction interface, situated near to where the event horizon is expected to form. The motivation for implementing this generalization arises from the fact that recent observations have confirmed an accelerated cosmic expansion, for which dark energy is a possible candidate.
Dark matter effects may be attributed to interactions between the Machian strings connecting every pair of elementary particles in the observable Universe. A simple model for the interaction between Machian strings is proposed. In the early Universe, the Machian strings of a density perturbation had a spherically symmetric distribution and the interaction with the Machian strings of a test particle is found to give a multiple of the Newtonian gravitational acceleration. In a strong gravitational field, the interaction between Machian strings tends to a constant limit in order to ensure the absence of dark matter effects in the Solar System. Dark matter effects on a galactic scale may be attributed to a change in the distribution of the Machian strings around a galaxy during the process of galaxy formation. The interaction between the Machian strings of a test mass and the Machian strings of a galaxy is considered in detail and the MOND phenomenology for galaxy rotation curves is obtained.
It was recently shown that gravitons with a very small mass should have formed a Bose-Einstein condensate in the very early Universe, whose density and quantum potential can account for the dark matter and dark energy in the Universe respectively. Here we show that the condensation can also naturally explain the observed large scale homogeneity and isotropy of the Universe. Furthermore gravitons continue to fall into their ground state within the condensate at every epoch, accounting for the observed flatness of space at cosmological distances scales. Finally, we argue that the density perturbations due to quantum fluctuations within the condensate give rise to a scale invariant spectrum. This therefore provides a viable alternative to inflation, which is not associated with the well-known problems associated with the latter.
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We consider a toy model for the supermassive compact object at the galactic center that does not require the presence of a black hole. We assume a matter distribution of weakly interacting particles with a density profile inferred from dark matter profiles in the outer regions. We show that rotation curves close to the center of the Milky Way galaxy can be explained within this model. We also show that the motion of test particles (stars) at distances of the order of 100 astronomical units can not be distinguished from the motion of corresponding particles in the Schwarzschild geometry. However, differences arise at shorter distances, suggesting that it could be possible to observationally test the validity of the model in the near future.
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