Other studies have strongly suggested that galaxy rotation curves remain flat indefinitely for as far as they can be observed. This study claims that they decline in a Keplerian manner at the extremes of their outer portions.
Jeans-based measurements of the Milky Way (MW) rotation curve (RC) have revealed a declining outer RC. The interpretation, however, depends sensitively on the tracer selection, the tracer density profile, gradient terms in the Jeans equation, and non-axisymmetric perturbations in the outer disk.
We present a more self-consistent Jeans analysis of the MW RC and reassess whether the outer decline remains after a revised treatment of the main Jeans terms and their associated systematic uncertainties, including those related to non-axisymmetric perturbations. We select a kinematically homogeneous disk tracer sample designed to retain stars on nearly circular disk orbits, removing only 12% of the original sample. We estimate the tracer density profile from the same stars used for the kinematic moments, rather than adopting an external scale length.
We find that the tracer density profile is better described by a double exponential over the validated range 12.5 < R < 21 kpc. We also assess the main systematic uncertainties associated with the fiducial Jeans equation terms, including the often neglected cross term, and account for different rotational velocities in the outer disk substructures. The derived RC remains nearly flat in the inner disk and declines at large radii. Over the adopted outer interval, R≳16kpc, the RC slope is consistent with a Keplerian decline even after accounting for the systematic uncertainties. The corresponding mass modeling gives an extrapolated dynamical mass of 2.01 +0.10 −0.08 × 10^11M⊙.
Yongjun Jiao, Francois Hammer, Istiak Akib, Yanbin Yang, Haifeng Wang, "A Self-Consistent Jeans Analysis of the Milky Way Rotation Curve" arXiv:2609.30364 (September 24, 2026) (accepted by The Astrophysical Journal, September the 19th 2026).
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