Implications of the Milky Way Declining Rotation Curve

TL;DR

The paper reports a sharply declining rotation curve for the Milky Way based on Gaia DR3 data, challenging dark matter halo models and suggesting the need for alternative explanations like circumgalactic plasma gas.

Contribution

It presents the first observation of a declining Milky Way rotation curve and analyzes its implications for galaxy mass estimates and dark matter models.

Findings

Milky Way's rotation curve sharply declines after 16 kpc.

Total mass of the Milky Way is significantly lower than standard dark matter estimates.

Modified gravity fits suggest a lower total mass consistent with visible baryons.

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, $(2-5)\times10^{12}M_\odot$. 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 $M\sim1.3\times 10^{11}M_{\odot}$, while the Newtonian fit predicts a mass of $M\sim2\times 10^{11}M_{\odot}$. 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.