Self-Consistent Jeans Modeling Shows Keplerian Decline in Milky Way Rotation Curve Beyond 16 kpc
A homogeneous disk-tracer Jeans analysis finds the Milky Way rotation curve declines at large radii in a manner consistent with Keplerian motion after accounting for density-profile and perturbation uncertainties. The implied dynamical mass is 2.01^{+0.10}_{-0.08} × 10^{11} M_⊙. The key advance is measuring the tracer density from the same stars used for kinematics.
The study reprocesses Gaia DR3 and other kinematic catalogs by retaining stars on nearly circular orbits after removing only 12% of the sample. Tracer density is measured directly from the same stars rather than an external scale length, producing a double-exponential profile between 12.5 and 21 kpc. All major Jeans terms, including the previously neglected cross term, are evaluated together with non-axisymmetric perturbations from known outer-disk substructures.
The derived rotation curve remains flat inside ~12 kpc but drops at larger radii even after systematic uncertainties are folded in. Mass modeling of the declining segment produces a total dynamical mass lower than most recent estimates that assumed a flat outer curve. This result hinges on the self-consistent density profile and careful treatment of substructure velocities.
Earlier Jeans analyses reached conflicting conclusions largely because they imported external density laws or ignored gradient cross terms. The present approach reduces those systematics and shows the outer decline survives. Future wide-field spectroscopic surveys that enlarge the homogeneous tracer sample at R > 18 kpc can test whether the Keplerian slope persists or flattens again.
Gaia DR4 kinematic release: the measured outer slope will remain steeper than -3 km s^{-1} kpc^{-1} at 5-sigma if the Keplerian interpretation holds.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2609.30364)
- [2]Supporting Source(https://ui.adsabs.harvard.edu/abs/2023ApJ...949...44E)