The Persistent Problem of Spiral Galaxies

The current explanation for spiral galaxies is that density waves in a spiral form rotate through the disks of these galaxies, continually forming new arms of hot bright stars and excited gas. The discussion here shows that many observed properties of spiral galaxies contradict this assumed density wave mechanism. Alternatively, it has been clear since the early 1950's that galaxies characteristically eject material from their nuclei. A number of astronomers have presented evidence that it is those ejections from the central regions of rotating galaxies that are responsible for the spiral arms. The evidence is reviewed and evaluated here, and it is concluded that the form and nature of the arms, their magnetic fields and rotational velocity characteristics, can best be explained by ejections of material, including plasma, from which the spiral arm stars are formed. This conclusion furnishes an answer to the long-standing problem of how the magnetic fields arise in the outer regions of spirals. Perhaps most importantly, the formation and renewal of spiral arms by ejection of plasma does not require them to be in rotation only under the pull of gravitational forces. If rotational energy is transferred to outer regions by ejections, the current interpretation of rotation curves may overestimate masses of spiral galaxies. If the problem of "missing mass" is diminished, so is the necessity for exotic suggestions to account for this undetected matter.     

Interpretation of Rotation Curves of Spiral Galaxies in Modified Teleparallel Gravity

There is a significant difference between the calculation based on the theory of general relativity and observation of rotation curves of spiral galaxies. To describe this discrepancy, two distinct theories have been proposed so far: existence of dark matter and modification of underlying gravitational theory. In the absence of dark matter, it is assumed that the theory of general relativity on galactic scales needs to be modified. This letter is devoted to explaining this difference in a modified teleparallel gravity. We show that modified teleparallel gravity favors flatness of rotation curves of spiral galaxies much in the same way as observation shows.     

Interpretation of Rotation Curves of Spiral Galaxies in Modified Teleparallel Gravity

There is a significant difference between the calculation based on the theory of general relativity and observation of rotation curves of spiral galaxies. To describe this discrepancy, two distinct theories have been proposed so far： existence of dark matter and modification of underlying gravitational theory. In the absence of dark matter, it is assumed that the theory of general relativity on galactic scales needs to be modified. This letter is devoted to explaining this difference in a modified teleparMIeI gravity. We show that modified teleparallel gravity favors flatness of rotation curves of spiral galaxies much in the same way as observation shows.     

The Carmeli Metric Correctly Describes Spiral Galaxy Rotation Curves

The metric by Carmeli accurately produces the Tully-Fisher type relation in spiral galaxies, a relation showing the fourth power of the rotation speed proportional to the mass of the galaxy. And therefore it is claimed that it is also no longer necessary to invoke dark matter to explain the anomalous dynamics in the arms of spiral galaxies. An analysis is presented here showing Carmeli’s 5 dimensional space-time-velocity metric can also indeed describe the rotation curves of spiral galaxies based on the properties of the metric alone.     

Magnetized spiral chains of plasmonic ellipsoids for one-way optical waveguides

When a linear chain of plasmonic nanoparticles is subject to longitudinal magnetic field, it exhibits optical Faraday rotation. If the magnetized nanoparticles are plasmonic ellipsoids arranged as a spiral chain, the interplay between the Faraday rotation and the geometrical spiral rotation (structural chirality) can strongly enhance nonreciprocity. This interplay forms a waveguide that permits one-way propagation only, within four disjoint frequency bands, two bands for each direction.     

Darwin curves and galaxy arms

In the natural world, there exists one kind of structure which is beyond the scope of human laboratorial experiment. It is the structure of galaxies which is usually composed of billions of stars. Spiral galaxies are flat disk-shaped. There are two types of spiral galaxies. The spiral galaxies with some bar-shaped pattern are called barred spirals, and the ones without the pattern are called ordinary spirals. Longer-wavelength galaxy images (infrared, for example) show that ordinary spiral galaxies are basically an axi-symmetric disk that is called exponential disk. For a planar distribution of matter, Jin He defined Darwin curves in the plane as such that the ratio of the matter densities at both sides of the curve is constant along the curve. Therefore, the arms of ordinary spiral galaxies are Darwin curves. Now an important question is that: Are the arms of barred spiral galaxies the Darwin curves too? Fortunately, Jin He designed a piece of Galaxy Anatomy graphic software. With the software, not only can people simulate the stellar density distribution of barred spiral galaxies but also can draw the Darwin curves of the simulated galaxy structure. This paper shows partial evidence that the arms of galaxy NGC 3275, 4548 and 5921 follow Darwin curves.     

Inhomogeneous exact solution in brane gravity and its applications

Considering an inhomogeneous brane embedded in a five dimensional constant curvature bulk, we find the non-static and spherically symmetric exact solutions of the Einstein equations on the brane. With different choices of the parameters, one interesting case/solution is studied. We show that an inhomogeneous brane model can explain the accelerated expansion of the universe at large distance scales and also the galaxy rotation curves of spiral galaxies without assuming the existence of dark matter or new modified theories at the galactic scales.     

Does a Kalb–Ramond field make spacetime optically active?

A spacetime with torsion produced by a Kalb–Ramond field coupled gravitationally to the Maxwell field, in accordance with a recent proposal by two of us (PM and SS), is argued to lead to optical activity in synchrotron radiation from cosmologically distant radio sources. We show that this indicates a very small, but possibly observable rotation of the plane of polarization of the radiation, above and beyond the Faraday rotation due to magnetized galactic plasma. Implications for heterotic string theory are outlined. Received: 27 October 2001 / Published online: 25 January 2002     

星系磁场和星系激波演化的一种模式

本文求解了二维不定常磁流体力学方程组,从而讨论星系磁场和星系激波的起源和演化过程。初始均匀的磁场将缠卷而在星系盘中形成螺旋形的结构,其中磁场和星际气体是冻结在一起的。分析了星际磁场对形成星系激波的影响。由于磁场不是很强,它对星系激波的影响不是非常强。     

A linear theory of resonance structures in spiral galaxies

The resonance mechanism for the formation of galactic spirals is considered. Expressions are derived for the resonance responses of disks with circular and nearly circular stellar orbits. The spiral responses produced by the central oval-shaped structures (bars) available in many galaxies are shown to have the characteristic properties of the spirals observed in these galaxies. In the most interesting case of a quasi-steady state, the spiral responses possess a similarity property: the spiral thickness and inclination are proportional to the mean size of an epicycle (an analog of the Larmor circle in plasma).     

Nonlinear spiral waves in a galactic disk

An analytical solution of the nonlinear dynamic equations for a galactic disk is found. This solution describes the spiral design of spiral galaxies. The logarithmic profile of the spiral design and relatively larger density fluctuations as compared to velocity-field fluctuations are explained. Breaking of the obtained solution takes place for a certain critical amplitude. This can be a mechanism for the formation of galactic shocks and narrow star formation regions.     

Violation of the Greisen-Zatsepin-Kuzmin cutoff: a tempest in a (magnetic) Teapot? Why cosmic ray energies above 10(20) eV may not require new physics

The apparent lack of suitable astrophysical sources for the observed highest energy cosmic rays within approximately 20 Mpc is the "Greisen-Zatsepin-Kuzmin (GZK) paradox." We constrain representative models of the extragalactic magnetic field structure by Faraday rotation measurements; limits are at the microG level rather than the nG level usually assumed. In such fields, even the highest energy cosmic rays experience large deflections. This allows nearby active galactic nuclei (possibly quiet today) or gamma ray bursts to be the source of ultrahigh energy cosmic rays without contradicting the GZK distance limit.     

Rotation curves of galaxies: Missing mass or missing physics

The rotation curves of galaxies are modelled using very special properties of an hydrodynamically turbulent fluid possessing helicity fluctuations. The development of correlations among these fluctuations leads to the formation of organized structures characterized by a new flat branch of the spatial energy spectrum in addition to the well known Kolmogorov spectrum. It is proposed that the flat nature of the rotation curves of galaxies may be a result of the energy cascading processes occuring in turbulent galactic atmospheres. Thus, in this model, there is no need of invoking dark matter to account for the flat rotation curves of galaxies.     

Special features of galactic dynamics: Disc dynamics

This is a tutorial presentation of special features of galactic disc dynamics, which completes our introduction to galactic dynamics initially presented in [30]. The emphasis is on topics where galactic dynamics and celestial mechanics share common starting points and/or methods of approach. We start by giving some definitions and general notions on the link between observations and dynamical modeling of discs. Then we focus on the application of resonant Hamiltonian perturbation theory in disc resonances. By examining in detail the case of the Inner Lindblad resonance, we demonstrate how resonant perturbation theory leads to an orbital theory of spiral structure in normal galaxies. Passing to barred galaxies, the phase space structure and the role of chaos in the corotation region are analyzed. This is accomplished by a summary of the modern theory of invariant manifolds of unstable periodic orbits in the vicinity of L₁ or L₂, which can interpret the generation of spiral patterns by chaotic orbits beyond corotation. Some additional topics, potentially important for disc dynamics, are briefly commented.     

Impact of a global quadratic potential on galactic rotation curves

We present a conformal gravity fit to the 20 largest of a sample of 110 spiral galaxies. We identify the presence of a universal quadratic potential V(κ)(r)=-κc2r2/2 with κ=9.54×10??? cm?2 induced by cosmic inhomogeneities. When V(κ)(r) is taken in conjunction with both a universal linear potential V(γ?)(r)=γ?c2r/2 with γ?=3.06×10?3? cm?1 generated by the homogeneous cosmic background and the contribution generated by the local luminous matter in galaxies, the theory then accounts for the rotation curve systematics observed in the entire 110 galaxies, without the need for any dark matter whatsoever. Our study suggests that using dark matter may be nothing more than an attempt to describe global effects in purely local galactic terms. With V(κ)(r) being negative, galaxies can only support bound orbits up to distances of order γ?/κ=100kpc, with global physics imposing a limit on the size of galaxies.     

The Hubble law and the spiral structures of galaxies from equations of motion in general relativity

Fully exploiting the Lie group that characterizes the underlying symmetry of general relativity theory, Einstein's tensor formalism factorizes, yielding a generalized (16-component) quaternion field formalism. The associated generalized geodesic equation, taken as the equation of motion of a star, predicts the Hubble law from one approximation for the generally covariant equations of motion, and the spiral structure of galaxies from another approximation. These results depend on the imposition of appropriate boundary conditions. The Hubble law follows when the boundary conditions derive from the oscillating model cosmology, and not from the other cosmological models. The spiral structures of the galaxies follow from the same boundary conditions, but with a different time scale than for the whole universe. The solutions that imply the spiral motion areFresnel integrals. These predict the star's motion to be along the “Cornu Spiral.” The part of this spiral in the first quadrant is the imploding phase of the galaxy, corresponding to a motion with continually decreasing radii, approaching the galactic center as time increases. The part of the “Cornu Spiral” in the third quadrant is the exploding phase, corresponding to continually increasing radii, as the star moves out from the hub. The spatial origin in the coordinate system of this curve is the inflection point, where the explosion changes to implosion. The two- (or many-) armed spiral galaxies are explained here in terms of two (or many) distinct explosions occurring at displaced times, in the domain of the rotating, planar galaxy.     

Faraday Rotation of Overdense Magnetized Plasma

In this study, we investigate Faraday rotation of electromagnetic waves that are anomalously transmitted through an over‐dense magnetized plasma layer. Here, magnetized plasma indicates that the plasma layer is immersed in a uniform magnetic field. Firstly, normally opaque over‐dense magnetized plasma is shown to be transparent to obliquely incident electromagnetic waves. This high transparency can be achieved by providing conditions for resonant excitations of plasmonic modes. The resonant characteristics of the transmission coefficient of the considered structure are determined and discussed. The conditions under which the magnetized plasma behaves as a complete reflector are also obtained. Faraday rotation is shown to be enhanced under high transparency conditions. The reflected wave also exhibits Faraday rotation and is enhanced under total reflection conditions. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Landau excitation of spiral density waves in an inhomogeneous disk of stars

Drift-resonant Landau excitation of spiral density waves in a stellar disk of flat galaxies is proposed. This excitation of waves is suggested as a mechanism for the formation of structural features such as spiral arms and the slow dynamical relaxation of galaxies in a regime of hydrodynamical Jeans-type stability.     

Letter: An Einstein-Like Theory of Gravity with a Non-Newtonian Weak-Field Limit

We propose a model describing Einstein gravity coupled to a scalar field with an exponential potential. We show that the weak-field limit of the model has static solutions given by a gravitational potential behaving for large distances as ln & ThinSpace;r. The Newtonian term GM/r appears only as subleading. Our model can be used to give a phenomenological explanation of the rotation curves of the galaxies without postulating the presence of dark matter. This can be achieved only by giving up the Einstein equivalence principle at galactic scales.     

Spiral galaxies rotation curves with a logarithmic corrected newtonian gravitational potential

We analyze the rotation curves of 10 spiral galaxies with a newtonian potential corrected with an extra logarithmic term. The logarithmic correction can have its origin from fundamental frameworks, like string theories or effective models of gravity due to quantum effects. There is also a connection with some toy models resulting from TeVeS. We represent the spiral galaxies as a thin disk. There is a new constant associated with the extra term in the potential. The rotation curve of the chosen sample of spiral galaxies is well reproduced for a narrow range of the new constant. The compatibility of this correction with local physics is discussed.