Satellite Phase Space

The six-dimensional phase space distribution of the Milky Way's dwarf satellite galaxies — their positions, distances, and three-dimensional velocities — is far more structured and correlated than ΛCDM hierarchical assembly predicts. Beyond the planar spatial alignment already discussed, the satellites' velocity vectors are not randomly oriented but show systematic correlations: satellites in the Vast Polar Structure tend to have velocity components aligned with the plane's orbital sense, their velocity dispersions and orbital energies cluster in ways inconsistent with independent random accretion from the field, and the overall phase space distribution has lower entropy than simulated CDM satellite populations at equivalent mass scales. This excess phase space coherence implies either a common origin for many satellites or a physical organizing principle operating at formation, neither of which ΛCDM accommodates naturally.

Successive Collision Theory predicts excess phase space coherence as an inherent consequence of angular momentum inheritance. Satellites that formed from the same angular momentum stratum of the collision debris not only share spatial orbital planes but also share similar orbital energies, because their formation radii in the debris field were correlated with their angular momentum magnitudes. The debris field produced by the superluminal collision had a smooth angular momentum-energy distribution set by the collision geometry and the initial density profiles of the two pockets. Structures condensing from nearby regions in this distribution arrive in the Milky Way's halo with similar energies and angular momenta, populating a restricted region of phase space rather than filling it isotropically. The observed phase space coherence of the satellite population is therefore a direct map of the angular momentum structure of the original collision debris.

The SCT prediction is quantitatively testable: the phase space distribution of satellites should be consistent with having been drawn from a low-dimensionality angular momentum distribution, not from the high-dimensionality distribution of random CDM accretion events. Full six-dimensional proper motion data from Gaia for the complete satellite population allows direct reconstruction of the phase space volume and comparison to both CDM predictions and the SCT angular momentum stratum model. Early results from Gaia-measured proper motions are already showing that satellite orbital poles cluster more tightly than expected from CDM accretion histories, consistent with the SCT inheritance picture.