Research
Breathing motion and spiral arms
Gaia DR3 data reveals a distinct pattern of compressing breathing motion a coherent, antisymmetric vertical motion of stars around the Milky Way's mid-plane aligned with the Local arm. Comparison with an N-body simulation suggests that this pattern indicates the Local arm is in a growth phase, while the expanding breathing motion observed near the Perseus arm may indicate it is in a disruption phase. These findings suggest that the Milky Way harbours dynamic spiral arms in various evolutionary phases.
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Bar resonances
The Gaia data reveal complex stellar velocity-space structures, such as the Hercules stream, which cannot be explained by axisymmetric models. Using an N-body simulation of a Milky Way-like galaxy, Asano et al. (2020, 2022) demonstrated that these substructures, including the Hercules stream, arise from bar resonances. We employed the Kullback-Leibler divergence to analyse the spatial and temporal variations of velocity-space distributions, finding that Hercules-like substructures are most prominent in specific regions in the bar's rotating frame, highlighting the dynamic influence of bar resonances on the stellar distribution.
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Vertical dynamics in the perturbed Galactic disc
Recent observations from the Gaia mission have revealed non-equilibrium vertical phase-space structures in the Milky Way disk (e.g vertical phase spirals, bending modes, and breathing modes) spurring extensive investigation into past encounters with satellite galaxies. Using high-resolution numerical simulations, we studied how tidal interactions with the Sagittarius dwarf galaxy shape the disc's vertical dynamics through the interplay of direct satellite impacts, internal structures, and disc self-gravity. Asano et al. (2025) demonstrates that direct satellite encounters initially excite bending modes while tidally inducing spiral arms, which indirectly drive longer-lived breathing modes and cause a progressive transition in the dominant vertical oscillation across the disc. Building on this dynamic framework, Asano & Antoja (2026) highlights the critical role of disc self-gravity, showing that it induces a delayed phase-mixing response.
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