Magnetohydrodynamic flows as Newtonian-type gravitational motions

Spyrou, N.; Tsagas, Christos G.

doi:10.2478/s11534-010-0004-1

Cited by 2 publications

(1 citation statement)

References 13 publications

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“…Furthermore, in the stellar and galactic levels, the notion of the repulsive gravity, predicted in the dynamical-equivalence approach, can be used to tackle problems like the formation of the (stellar and galactic) winds, and, in the case of magnetohydrodynamic flows, of the (stellar and galactic) jets [15] .…”

Section: Applicationsmentioning

confidence: 99%

Negative mass and repulsive gravity in Newtonian theory, and consequences

Spyrou¹

2009

J. Phys.: Conf. Ser.

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Abstract. In the context of the Newtonian theory of gravity, the dynamical equivalence of hydrodynamic flows with geodesic lines, in the interior of a bounded, gravitating perfect-fluid source, results in the possibility of negative mass and, hence, of repulsive gravity. The consequences are outlined for the overall picture of the Solar System and the large-scale cosmological, structures, and some predictions are attempted based on some current and mostly unexplained so far observational data. IntroductionAccording to many current observational data, the realistic picture and morphology of an astrophysical-cosmological structure differs greatly from its corresponding optical picture. This is true for the Solar System, whose linear dimensions are of the order of 10 5 AU, namely, approximately half the distance to the nearest star to the Sun, and also for the Milky Way, whose linear dimensions are at least 200 kpc, almost ten times larger than its optical linear dimensions (~30 kpc). Similar arguments hold for other types of galaxies and for even larger cosmological structures, namely, clusters of galaxies and super-clusters of galaxies. Therefore, it appears appropriate that the large-scale cosmological structures be treated as almost spherically symmetric, very complex, practically continuous, and of much larger linear dimensions cosmological structures than previously assumed. Consequently, the constituent elements of the Universe and the Universe as a whole, can quite satisfactorily be treated as continuous gravitational systems and, more specifically, bounded, gravitating perfect-fluid sources, the physical-dynamical description of which is very well established at both the Newtonian and the general-relativistic levels. So, we arrive at the very crucial result, that the motions of and in these constituents should be considered as hydrodynamic flows rather than geodesic motions. Now, in view of the wealth of such observational data and strong indications, it has been suggested [1,14] that, in both the Newtonian and the general-relativistic theories of gravity, and at all levels, namely, cosmological [1,7,8,9,10,13], galactic [1,2,3,5,6,7,8,10,11], and stellar [1,2,4,6], it is possible to give to the equations of hydrodynamic (and hydromagnetic) flow motions in the interior of a bounded gravitating perfect-fluid source the form of the equations of the equations of geodesic motion in it. This approach is usually referred to as the dynamical-equivalence approach.It is exactly this dynamical-equivalence approach, that enables us to recast the geodesic motions, mostly applied in the observational determination of masses, now taking into account, as sources of geodesic motions, not simply the mass density but all of the source's internal physical characteristics (like e.g. mass density, pressure, internal thermodynamic energy, velocities of both ordered and statistical thermodynamic motions). Similarly, this approach enables us to determine the contribution

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Section: Applicationsmentioning

confidence: 99%

Negative mass and repulsive gravity in Newtonian theory, and consequences

Spyrou¹

2009

J. Phys.: Conf. Ser.

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A conventional approach to the dark-energy concept

Kleidis

Spyrou

2011

A&A

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Motivated by results implying that the constituents of dark matter (DM) might be collisional, we consider a cosmological (toy-) model, in which the DM itself possesses some sort of thermodynamic properties. In this case, not only can the matter content of the Universe (the baryonic component, which is tightly gravitationally-bounded to the dark one, also being included) be treated as a classical gravitating fluid of positive pressure, but, together with all its other physical characteristics, the energy of this fluid's internal motions should be taken into account as a source of the universal gravitational field. In principle, this form of energy can compensate for the extra (dark) energy, needed to compromise spatial flatness, while the post-recombination Universe remains ever-decelerating. What is more interesting, is that, at the same time (i.e., in the context of the collisional-DM approach), the theoretical curve representing the distance modulus as a function of the cosmological redshift, μ(z), fits the Hubble diagram of a multi-used sample of supernova Ia events quite accurately. A cosmological model filled with collisional DM could accommodate the majority of the currently-available observational data (including, also, those from baryon acoustic oscillations), without the need for either any dark energy (DE) or the cosmological constant. However, as we demonstrate, this is not the case for someone who, although living in a Universe filled with self-interacting DM, insists on adopting the traditional, collisionless-DM approach. From the point of view of this observer, the cosmologically-distant light-emitting sources seem to lie farther (i.e., they appear to be dimmer) than expected, while the Universe appears to be either accelerating or decelerating, depending on the value of the cosmological redshift. This picture, which, nowadays, represents the common perception in observational cosmology, acquires a more conventional interpretation within the context of the collisional-DM approach.

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Magnetohydrodynamic flows as Newtonian-type gravitational motions

Cited by 2 publications

References 13 publications

Negative mass and repulsive gravity in Newtonian theory, and consequences

Negative mass and repulsive gravity in Newtonian theory, and consequences

A conventional approach to the dark-energy concept

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