Mass density and size estimates for spiral galaxies using general relativity
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Data
2017
Autores
Magalhaes, N. S. [UNIFESP]
Cooperstock, F. I.
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Resumo
Rotation curves of spiral galaxies reveal a physical phenomenon that has been seen to lack a satisfactory scientific explanation: velocities of stars far from the nucleus are high and approximately constant. In the context of Newtonian dynamics, the existence of a new kind of matter (dark matter) is assumed, which, when added to the usual observed matter, would account for the phenomenon; however, the nature of such dark matter is unknown and it was never detected. There are other ongoing investigations of the phenomenon, such as MOND and emergent gravity. In this work we present new results from another approach, in which general relativity is employed to approximate a galaxy by an axially-symmetric, pressure-less fluid in stationary rotation, yielding an expression for its rotation curve and mass density. We apply this model to data of four galaxies: NGC 2403, NGC 2903, NGC 5055 and the Milky Way. We obtain mass density contours of these galaxies which we compare to observational data, a procedure that could open a new window for investigating galactic structure. In our Solar neighborhood, we found a mass density and density fall-off fitting observational data satisfactorily, addressing a critique to the model by Fuchs and Phleps. Using a threshold density apparently related to the observed optical zone of a galaxy, the model had already indicated that the Milky Way could be larger than had been believed to be the case. To our knowledge, this was the only such existing theoretical indication ever presented. Recent observational results by Xu et al. have confirmed that theoretical prediction, which we fortify here using a large set of observational data. Galactic masses are seen to be higher than the baryonic mass determined from observations but lower than those deduced from the approaches relying upon dark matter in a Newtonian context. We also calculate the non-luminous fraction of matter for our sample of galaxies and present possible general relativistic explanations for this. The evidence points to general relativity playing a significant role in the explanation of the phenomenon.
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Astrophysics And Space Science. Dordrecht, v. 362, n. 11, p. -, 2017.