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The Milky Way’s plane of satellites is consistent with ΛCDM

Sawala, Till; Cautun, Marius; Frenk, Carlos; Helly, John; Jasche, Jens; Jenkins, Adrian; Johansson, Peter H.; Lavaux, Guilhem; McAlpine, Stuart; Schaller, Matthieu

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Till Sawala

Marius Cautun

Jens Jasche

Peter H. Johansson

Guilhem Lavaux

Stuart McAlpine

Matthieu Schaller


The Milky Way is surrounded by 11 ‘classical’ satellite galaxies in a remarkable configuration: a thin plane that is possibly rotationally supported. Such a structure is thought to be highly unlikely to arise in the standard (ΛCDM) cosmological model (Λ cold dark matter model, where Λ is the cosmological constant). While other apparent discrepancies between predictions and observations of Milky Way satellite galaxies may be explained either through baryonic effects or by invoking alternative forms of dark matter particles, there is no known mechanism for making rotating satellite planes within the dispersion-supported dark matter haloes predicted to surround galaxies such as the Milky Way. This is the so-called ‘plane of satellites problem’, which challenges not only the ΛCDM model but the entire concept of dark matter. Here we show that the reportedly exceptional anisotropy of the Milky Way satellites is explained, in large part, by their lopsided radial distribution combined with the temporary conjunction of the two most distant satellites, Leo I and Leo II. Using Gaia proper motions, we show that the orbital pole alignment is much more common than previously reported, and reveal the plane of satellites to be transient rather than rotationally supported. Comparing with new simulations, where such short-lived planes are common, we find the Milky Way satellites to be compatible with standard model expectations.


Sawala, T., Cautun, M., Frenk, C., Helly, J., Jasche, J., Jenkins, A., …Schaller, M. (2023). The Milky Way’s plane of satellites is consistent with ΛCDM. Nature Astronomy, 7(4), 481-491.

Journal Article Type Article
Acceptance Date Nov 3, 2022
Online Publication Date Dec 19, 2022
Publication Date 2023-04
Deposit Date Feb 13, 2023
Publicly Available Date May 30, 2023
Journal Nature Astronomy
Publisher Nature Research
Peer Reviewed Peer Reviewed
Volume 7
Issue 4
Pages 481-491


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