Narrow Results

In this paper, I show that the generally accepted methods of classical mechanics are not applicable for calculating the outer parts of the rotation curves (RCs) of galaxies, where the influence of collisions on gas dynamics becomes dominant. In addition, the hydrodynamic approach cannot be used for this purpose due to an extreme rarefaction of the gas. I develop a new approach for describing the gas dynamics in outer regions of galactic disks, where the gas dynamics is determined mainly by collisions. Equations (free from restrictions imposed on hydrodynamics) are obtained that describe the dynamics of rarefied gas. The resulting equation $\frac{D}{n}\frac{1}{R_0}\frac{\partial n}{\partial r}=-\sqrt{(V_{d\perp }{V}_{\perp }^{\mathrm{\text{tot}}})}$ (14) relates two quantities: the tangential velocity of the gas as a function of the distance from the center of a galaxy (RC) and the radial distribution of the gas density.

It is shown that if the physical properties of the rarefied gas are properly taken into account, then dark matter (DM) is not required, and the “nonphysical” (non-Keplerian) RCs of the outer parts of the galactic disks are tailwinds that can be described within the framework of conventional gas kinetics. To illustrate the correctness of the obtained model, two galaxies with flat RCs (NGC7331 and NGC3198) are considered. From the observed RCs, using Eq. (14), the radial densities of the gas are calculated. An excellent agreement was obtained between the calculated gas densities and their observed values, which is a serious argument in favor of the developed model. Thus, the nonphysical RCs of spiral galaxies represent the tailwinds of gas, the dynamics of which is naturally described by the kinetic equation without involving the concept of DM.

Total masses of two galaxies NGC7331 and NGC3198 have been calculated. Implications for cosmology are discussed.

Two problems related to dark matter are considered in the context of a braneworld model in which the confinement of gauge fields on the brane is achieved by invoking a confining potential. First, we show that the virial mass discrepancy can be addressed if the conserved geometrical term appearing in this model is considered as an energy–momentum tensor of an unknown type of matter, the so-called X-matter whose equation of state (EoS) is also obtained. Second, the galaxy rotation curves are explained by assuming an anisotropic energy–momentum tensor for the X-matter.

In this paper, we find a four-dimensional metric for a large black hole immersed in dark matter. Specifically, we look for and find a static spherically symmetric black hole solution to the Einstein equations which gives, in the Newtonian limit, the rotation curves of galaxies, including the flat region and the baryonic Tully–Fisher relation, and which has a regular horizon. We obtain as well the energy–momentum tensor of the dark matter sourcing this spacetime and it turns, in special, to satisfy the four energy conditions (dominant, weak, null and strong) everywhere outside the horizon. This black-hole-dark-matter system represents a successful simplified model for galaxies, opens a new area for exploring the relativistic regime of dark matter, and shows that the theory of General Relativity together with dark matter can account for the rotation curves of galaxies.

We study the effect of the extrinsic curvature on the rotation curves within the context of brane-world, in a 5-d bulk with constant curvature. The covariant equations of motion for the brane-world are applied to determine the modified Newtonian potential approximation and the velocity curve. We consider a static disk galaxy which is composed only of ordinary visible matter. Using the Weyl static metric as a model, we find that the velocity curve is given by the square root of a small power of the radial distance to the galactic core.

In the young field of constructive gravity, the gravity theory constructed from general linear electrdynamics has been frequently used as a physically meaningful text case for the entire approach. Based on a Newtonian approximation of area metric gravity, we use the rotation curves of low surface brightness galaxies to determine ranges for the gravitational constants in this weak field limit. Thus we are able to show that even by using very simple models for the distribution of visible matter in the galaxies, Newtonian area metric gravity yields reasonable rotation curves and consistent estimates for the gravitational constants. Area-metric gravity turns out to not be an alternative to dark matter, but to reduce the dark matter fraction and to remove the need for a distribution subtantially different from visible matter.

General relativity and quantum theory are believed to be incompatible, but are they? Here it is revealed that there is a logical way for these theories to be extended to a unified theory. In a fresh approach, the graviton is defined as the quantum field particle that produces the dimensions of time and space, whereby gravitational effects are one consequence of this role. The concept is explained and evidence is revealed which supports the new direction. The approach leads to the derivation of the Einstein equation of general relativity and the unification equation, which predicts that the frequency of gravitons in the void is f_X0=1.48 × 10⁴² s⁻¹. Thus the graviton is a high-energy particle, quite the opposite to expectations of current particle theory, but in keeping with its role of producing: the dimensions of time and space, vacuum energy, expansion of the Universe, and gravitational effects. The predicted frequency is accurately supported by empirical data from cosmological measurements. Observations that have been attributed to dark matter and vacuum energy, are now explained by scattering of gravitons and diffraction patterns of gravitons. Diffraction minima have reduced energy density, thus producing microscopic regions of curvature of spacetime in galactic haloes. Based of these diffraction patterns, equations are derived which accurately predict the rapid speed of orbiting bodies and explain the flatness of rotation curves. The evidence supports the extension of quantum theory and general relativity to a general quantum theory.

We employed general relativity (GR) successfully to describe the galactic velocity profiles. In this work we present a mapping of the density contours of galaxies, achieving good concordance with observational data. In our Solar neighbourhood, we found a mass density and density fall-off fitting observational data satisfactorily. Galactic masses are consistently seen to be lower than those deduced from the approaches relying upon dark matter. Our results indicate that GR is the key to an explanation of the stars’ high velocities in galaxies. Mapping galactic density contours directly from the dynamics opens a new window for predicting galactic structure.

Flat or almost flat rotation curves of spiral galaxies can be explained by logarithmic gravitational potentials. The field equations of GR admit of spacetime metrics with such behaviors. The scenario can be interpreted either as an alternative theory of gravitation or, equivalently, as a dark matter paradigm. In the latter interpretation, one is led to assign a dark companion to the baryonic matter who's size and distribution is determined by the mass of the baryons. The formalism also opens up a way to support Milgrom's idea that the acceleration of a test object in a gravitational field is not simply the newtonian gravitational force g_N, but rather an involved function of (g_N/a₀), a₀ MOND's universal acceleration.