On the relevance of chaos for halo stars in the Solar Neighbourhood

TL;DR

This study investigates whether chaotic mixing significantly erases signatures of past galactic accretion in the Solar Neighbourhood, finding that most halo stars do not exhibit rapid chaos-induced diffusion within a Hubble time.

Contribution

The paper demonstrates that chaotic mixing is less effective in erasing phase space signatures of accretion events than previously thought, based on cosmological simulations and analytical models.

Findings

Most halo stars have chaos onset times longer than a Hubble time.

Stars showing chaos do not diffuse significantly in phase space within a Hubble time.

Chaotic mixing may not be as relevant for erasing accretion signatures as previously assumed.

Abstract

We show that diffusion due to chaotic mixing in the Neighbourhood of the Sun may not be as relevant as previously suggested in erasing phase space signatures of past Galactic accretion events. For this purpose, we analyse Solar Neighbourhood-like volumes extracted from cosmological simulations that naturally account for chaotic orbital behaviour induced by the strongly triaxial and cuspy shape of the resulting dark matter haloes, among other factors. In the approximation of an analytical static triaxial model, our results show that a large fraction of stellar halo particles in such local volumes have chaos onset times (i.e., the timescale at which stars commonly associated with chaotic orbits will exhibit their chaotic behaviour) significantly larger than a Hubble time. Furthermore, particles that do present a chaotic behaviour within a Hubble time do not exhibit significant diffusion in phase space.