Implications of the Milky Way Declining Rotation Curve

Abstract

Almost all spiral galaxies have been observed to have flattening rotation curves. The new Gaia DR3 released data shows a Milky Way sharply Keplerian declining rotation curve, starting at $\sim 16$ kpc and ending at 26.5 kpc. The data reduces the total Milky Way mass by an order of magnitude, $M=2.06\times 10^{11}{M}_{\odot }$, compared to the standard required dark matter halo mass, $(2-5)\times 10^{12}{M}_{\odot }$. Newtonian and modified gravity (MOG) fits are applied to the Gaia DR3 rotation curve data. The fit obtained using MOG has a total mass of $M\sim 1.3\times 10^{11}{M}_{\odot }$, while the Newtonian fit predicts a mass of $M\sim 2\times 10^{11}{M}_{\odot }$. These are in excess of the estimated visible baryon mass of the Milky Way, $M_b\sim (0.6-1.0)\times 10^{11}{M}_{\odot }$. It is possible that if the cicumgalactic (CGM) plasma-gas continues to be confirmed experimentally, then the additional baryon mass required to account for the estimated total Milky Way mass could be attributed to the CGM hot plasma-gas halo.

8 pages, 2 figures

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