The flatness of the rotation curve of the Milky Way is challenged

Sabine Hossenfelder (see this) told about the recent findings challenging the view that the rotation curve of the Milky Way is flat. The findings are discussed in the article "The rotation Curve of the Milky Way: State of the Art, the Keplerian Decline Debate, and Implications for Dark Matter" by Alexandro Melchiorri and Ruchika (see this).

Here is part of the abstract of the article:

For four decades, the roughly flat rotation curve (RC) of the Milky Way (MW) stood as local evidence for an extended dark matter (DM) halo. Gaia DR3 has changed the picture: several analyses now find a velocity decline beyond R ≈ 15 kpc, and the most radical interpreta&t/sub>imes;tion claims a nearly Keplerian fall-off (v ∝ R^-1/2) that excludes a flat RC at 3σ and implies a total dynamical mass of only ≈ 2 × 10¹¹M_sun---three to five times below pre-Gaia estimates.

Taken at face value, this would make the MW exceptional among comparable spirals and challenge both ΛCDM and MOND. It would also alter predictions for direct-detection experiments, although the local DM density is not fixed by virial mass alone.

The findings challenge not only the ΛCDM model and MOND but also the TGD view of the galaxies, galactic dark matter, and galaxy formation (this).

1. The model relies on the identification of galactic dark matter as volume energy and Kähler magnetic energy assignable to long cosmic strings orthogonal to the galactic plane. Also cosmic strings parallel to the plane can be considered and collisions of nearly orthogonal cosmic strings could have given rise to spiral galaxies.

   Galaxies would correspond to tangles along the cosmic strings. Thickening of the cosmic string would have liberated energy and produced ordinary matter somewhat like in the decay of the inflaton field in cosmic inflation. The cylindrical geometry of the model predicts flat velocity spectrum but also implies testable deviations from the halo model.

2. First some numbers are needed. The radius of the visible part of the Milky way is about R=100,000 ly. The critical distance at which the rotation curve ceases to be flat is 15 kpc, that is 48,923 light-years, roughly R/2. The average distance between galaxies is L= 1-few million ly and suggests that the average distance of galaxies along cosmic strings is roughly L.
3. In the modification of Λ CDM, the dark mass halo should be concentrated near the centre. This implies that the dark matter of the galaxy is about 3/4 of the recent estimate and smaller than the cosmological average. For MOND the challenge is much more difficult to overcome. In TGD the galactic dark matter is along the long cosmic string.

In the TGD framework, one can consider several options as an explanation of the findings.

1. The monopole flux tubes are closed. If the return flux is along a single parallel monopole flux tube, there would be a violation of the planar asymmetry in the rotation curve caused by the weakening of gravitational force at one side and strengthening at the other side. The effect would increase at large distances. The rotation velocity would depend on the direction in the galactic plane and this might exclude the proposal.
2. The rotation curve is approximately flat if there is a kind of lattice of parallel cosmic strings orthogonal to the galactic plane. Triangular, square and hexagonal lattices can be considered. One can consider analogs of ferromagnets and antiferromagnets.
   1. The TGD view of dark matter as a phase with a larger h_eff suggests this kind of lattice as an interpretation. Manysheetedness with respect to CP₂ could mean this kind of lattice: different flux tubes would be sheets over CP₂. This option could be consistent with the cosmic estimate for the density of the dark matter.
   2. 15 kpc= 48,923 ly gives an idea about the density of parallel cosmic strings orthogonal to the galactic plane. The distance of cosmic strings should be larger but not too much so. The radius for the visible part of the Milky Way radius is 100,000 ly and roughly twice this scale so that the distance between cosmic strings should be larger than the radius of the visible galaxy.
   3. One could image a lattice of parallel cosmic strings with lattice spacing of 100-200 ly. Cosmic strings would have galaxies as tangles along them with average separation of 1-few million ly. The distance between parallel cosmic strings would be roughly by factor 1/10 smaller if it corresponds to galactic radius. Cylindrical symmetry is however violated. The effect is largest at large enough distances and should reflect the symmetry of the planar lattice.
3. One could think that the return flux is branched to less heavier flux tubes returning along a wall or could be also along thin cylindrical flux sheets. In this case, the effect of a constant cylindrical mass distribution would vanish in the entire interior. In the case of lattice this is not the case except along the cosmic string.

See the article About the recent TGD based view concerning cosmology and astrophysics or the chapter with the same title.