Local galactic gravity measured using Gaia star motions
Closed-Form of the Local Galactic Potential and Stellar Distribution Function from Gaia DR3
Machine Learning
Summary
Understanding how much dark matter is near our Sun is important for experiments trying to detect it, but previous estimates have disagreed a lot. This paper shows that trying to fit models for star motions and gravity at the same time doesn’t work well because it can’t tell which is right. Instead, the authors first estimate how stars move and then work out the gravitational force from those motions, finding formulas that describe the gravity near us. Their results for gravity match well with long-standing models of our galaxy’s disc, helping improve our understanding of the local dark matter environment.
dark matter densitydirect-detection experimentsstellar motionsGaia DR3Jeans theoremcollisionless Boltzmann equationdistribution functionlocal gravitational potentialsymbolic regressionself-gravitating isothermal disc
Authors
Indranil Das, Adam Kamoski, Dora Demiri, Brianna Isola, Hanieh Karimi, Dmitrii S. Zagorulia
Abstract
The local dark matter density determines the strength of the signal expected in direct-detection experiments, yet published estimates from stellar motions disagree by more than their errors, and the most recent machine-learning analysis of Gaia data finds a local density consistent with zero. According to Jeans' theorem, a distribution function built from integrals of motion satisfies the collisionless Boltzmann equation (CBE) trivially for any choice of potential, so a search that simultaneously fits the distribution function and the potential to the CBE identifies neither. Our pipeline instead estimates the distribution function in isolation, linearizing the equation in terms of accelerations and allowing for direct measurement of the local force field, and then fits closed forms to that field via symbolic regression. Throughout, we find that the usable information lies not in the CBE residual but in the stellar number counts, the observable most distorted by survey selection. Along the vertical profile, our recovered potential agrees with the classical self-gravitating isothermal disc.