Observing the Peculiar Acceleration of our Solar System with Quasar Proper Motions
Abstract
We measured the proper motion dipole of quasars observed by \textit{Gaia} to determine the acceleration of the Solar System with respect to the quasar rest frame. We characterised the full angular power spectrum of the proper motion field using the pseudo-Cℓ formalism and employed simulation-based inference to jointly constrain the dipole and higher multipole power. Cross-correlation with the \textit{Gaia} scanning strategy, stellar density and stellar proper motion maps was used to diagnose the origin of systematic power beyond the dipole. We applied this framework to both the \textit{Gaia} EDR3 quasar catalogue and the Quaia catalogue. The inferred acceleration is consistent with the previous determination, but the credible intervals widen by factors of 1.5 to 5 when higher-multipole degeneracies are properly marginalised, indicating that previous uncertainty estimates were optimistic. Our best estimate, based on the Quaia catalogue, is (gx, gy, gz) = (1.01+0.72−0.72, −4.94+0.54−0.55, −2.13+0.58−0.58) μas yr−1. This corresponds to an amplitude of 5.55−0.53+0.54 μas yr−1, where g = a/c is the Solar System acceleration expressed as a proper motion drift in equatorial coordinates. The inferred acceleration is directed towards (l, b) = (11.71+7.0−6.8, −9.01+7.0−6.9)∘, equivalently (α, δ) = (281.39+7.8−8.0, −22.93+6.5−6.2)∘. This is in good agreement with a Galactic centre--dominated acceleration. The acceleration components show no significant dependence on source redshift, providing further evidence of the acceleration's kinematic origin.
Versions
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BibTeX
@misc{nguyen2026observing,
title = {{Observing the Peculiar Acceleration of our Solar System with Quasar Proper Motions}},
author = {Phu Huy Nguyen and Calum Murray},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.30367},
eprint = {2605.30367},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.30367},
}
RIS
TY - UNPB
TI - Observing the Peculiar Acceleration of our Solar System with Quasar Proper Motions
AU - Phu Huy Nguyen
AU - Calum Murray
PY - 2026
DA - 2026/10/09
PB - arXiv
DO - 10.48550/arxiv.2605.30367
UR - https://arxiv.org/abs/2605.30367
AB - We measured the proper motion dipole of quasars observed by \textit{Gaia} to determine the acceleration of the Solar System with respect to the quasar rest frame. We characterised the full angular power spectrum of the proper motion field using the pseudo-C_ℓ formalism and employed simulation-based inference to jointly constrain the dipole and higher multipole power. Cross-correlation with the \textit{Gaia} scanning strategy, stellar density and stellar proper motion maps was used to diagnose the origin of systematic power beyond the dipole. We applied this framework to both the \textit{Gaia} EDR3 quasar catalogue and the Quaia catalogue. The inferred acceleration is consistent with the previous determination, but the credible intervals widen by factors of 1.5 to 5 when higher-multipole degeneracies are properly marginalised, indicating that previous uncertainty estimates were optimistic. Our best estimate, based on the Quaia catalogue, is (g_x, g_y, g_z) = (1.01^+0.72_−0.72, −4.94^+0.54_−0.55, −2.13^+0.58_−0.58) μas yr^−1. This corresponds to an amplitude of 5.55_−0.53^+0.54 μas yr^−1, where g = a/c is the Solar System acceleration expressed as a proper motion drift in equatorial coordinates. The inferred acceleration is directed towards (l, b) = (11.71^+7.0_−6.8, −9.01^+7.0_−6.9)^∘, equivalently (α, δ) = (281.39^+7.8_−8.0, −22.93^+6.5_−6.2)^∘. This is in good agreement with a Galactic centre--dominated acceleration. The acceleration components show no significant dependence on source redshift, providing further evidence of the acceleration's kinematic origin.
ER -