17 April 2017
ON THE GALAXY MOTIONS IN LANIAKEA SUPERCLUSTER ANGELO LOINGER AND TIZIANA MARSICO Abstract. The instance of the motions of the galaxies in LANIAKEA supercluster yields a clear illustration of the following results of general relativity: i) the trajectories of gravitationally interacting bodies are always geodesic; ii) there are always spacetime coordinates for which the trajectories of gravitationally and non-gravitationally interacting bodies are geodesic. This proposition can be extended to the case of presence of the Dark Matter.
KEYWORDS: galaxies; galaxy clusters; Great Attractors; Dark Matter. PACS: 04.20 – General relativity; 98.80 – Cosmology.
1. – A friend of us has remarked that our concise Note “Dark Matter, relativistic space-draggings and Weylian plasticine” [1] has been judged unpalatable by many physicists. Therefore, we publish now an application of its fundamental concept to the significant instance of the galaxy-supercluster LANIAKEA. [2]. In sects. 2 and 3 we recall various observed properties of LANIAKEA, and we reproduce the r´esum´e of paper [2]. In sect. 4 the motions of the galaxies in LANIAKEA are considered from the standpoint of general relativity.
2. – The diameter of LANIAKEA is equal to 5 × 108 light-years. There are ≈ 105 galaxies in this supercluster. The authors of [2] have succeeded in determining the peculiar (or proper ) motions of the galaxies, i.e. the motions which prescind from the expansion of the universe. It has been possible to determine the velocity flows of the galaxies, and consequently to individuate the gravitational attractor, which regulates the galaxy trajectories. As it is clear from the map of Fig.1 (which coincides with Fig.2 of [2]) the galaxies travel in filaments. A black point represents the Milky Way, which is situated at the periphery of LANIAKEA. We shall see in sect. 4 that general relativity can give na explanation of the structure of the great gravitational attractors in the superclusters.
3. – The authors of article [2] do not discuss the influence of the possible presence of Dark Matter on the galaxies of LANIAKEA. Therefore, the Date: 17 April 2017. 1
2
ANGELO LOINGER AND TIZIANA MARSICO
galaxy trajectories can be the result of the action of the standard gravitation plus the action of the Dark Matter. The analysis of the observed motions of the galaxies that we find in [2] is very subtle. For the present Note it is sufficient to reproduce the initial r´esum´e of [2], which gives the line of thought of the authors and the main results. “Galaxies congregate in clusters and along filaments, and are missing from large regions referred to as voids. These structures are seen in maps derived from spectroscopic surveys that reveal networks of structure that are interconnected with no clear boundaries. Extended regions with a high concentration of galaxies are called “superclusters”, although this term is not precise. There is, however, another way to analyse the structure. If the distance to each galaxy from Earth is directly measured, then the peculiar velocity can be derived from the subtraction of the mean cosmic expansion, the product of distance times the Hubble constant, from observed velocity. The peculiar velocity is the line-of-sight departure from the cosmic expansion and arises from gravitational perturbations; a map of peculiar velocities can be translated into a map of the distribution of matter. Here we report a map of structure made using a catalogue of peculiar velocities. We find locations where peculiar velocity flows diverge, as water does at watershed divides, and we trace the surface of divergent points that surrounds us. Within the volume enclosed by this surface, the motions of galaxies are inward after removal of the mean cosmic expansion and long range flows. We define a supercluster to be the volume within such a surface, and so we are defining the extent of our home supercluster, which we call Laniakea. A key component of this paper is an accompanying movie that can be viewed (also in 3D) and downloaded at http://irfu.cea.fr/laniakea or http://vimeo.com/pomarede/laniakea.”
4. – We have two possibilities for the motions of the galaxies in LANIAKEA: i ) The galaxy trajectories are determined only by gravitational interactions between the galaxies and with the central great attractor ii ) The trajectories are determined also by the Dark Matter and by nongravitational actions; in Note [1] we have hypothesized that the role of the Dark Matter can be played by the galaxy rotations (a Lense-Thirring effect on a gigantic scale). – Let us consider first the case i ). We have given exact demonstrations [3] that the gravitationally interacting particles of an ensemble have trajectories which are always geodesic; the presence of a massive or supermassive centre does not modify this result. It is very reasonable to apply these considerations to the translational motions of the galaxies in LANIAKEA. We see that general relativity determines perfectly the structure of the mentioned trajectories. – And now the case ii ).
ON THE GALAXY MOTIONS IN LANIAKEA SUPERCLUSTER
3
It was explicitly and repeatedly emphasized by Weyl [1] that Einsteinian spacetime is endowed with a typical plasticity. Consequently, it is continuously deformable, and we can deform it in such a way to give to the trajectories of material particles, gravitationally and non-gravitationally interacting, any prescribed form, in particular a geodesic one. This means that there exist systems of spacetime coordinates for which these trajectories are geodesic. We can apply this result to the galaxies of LANIAKEA. And we see that the geodesic character of their trajectories holds always for some reference frames. Remark that this conclusion is independent of any assumption on the Dark Matter, in particular it is independent of the assumption of Note [1]. The general theory of relativity is extraordinarily powerful, the Dark Matter becomes a by-product of some systems of coordinates. The general relativity can explain also the nature of the Great Attractors: as we have proved [4], under reasonable assumptions the final result of the gravitational collapse of a mass M is its concentration within a spherical surface of area 4π(2m)2 , where m ≡ GM/c2 . Therefore, a Great Attractor reveals itself only through its enormous gravitational attraction.
References [1] A. Loinger and T. Marsico, Academia.edu and ResearchGate, January 1, 2017. [2] B. Tully et alii, Nature, vol. 513, number 516, p.71 (4 September 2014). [3] A. Loinger and T. Marsico, see e.g., sects. 1 and 2 of “A detailed confutation etc.”, Academia.edu and ResearchGate, April 20, 2016. [4] A. Loinger and T. Marsico, Rend. Ist. Lomb., Cl. Sci. Mat. e Nat., vol. 146 (2014), p.229, sects. 5 of “On the relativistic gravitational collapse – et cetera ”. www.ilasl.org/index.php/Scienze/article/view/I99/202.
4
ANGELO LOINGER AND TIZIANA MARSICO
Figure 1. [Fig.2 of [2]]. A slice of the Laniakea Supercluster in the supergalactic equatorial plane. Shaded contours represent density values within the equatorial slice with red at high densities and blue in voids. Individual galaxies from a redshift catalog are given as white dots. Velocity flow streams within the Laniakea basin of attraction are shown in white. The orange contour encloses the outer limits of these streams. This domain has a extent of ∼ 12,000 km s−1 (∼ 160 Mpc diameter) and encloses ∼ 1017 M⊙ . ` di Milano, Via Celoria, 16 - 20133 A.L. – Dipartimento di Fisica, Universita Milano (Italy) T.M. – Liceo Classico “G. Berchet”, Via della Commenda, 26 - 20122 Milano (Italy) E-mail address:
[email protected] E-mail address:
[email protected]
View publication stats
