Scope: This is a lightweight, pedagogical N-body style visualization using test particles in the Galactic plane. It is not a full self-consistent dynamical model.
Geometry: Motion is 2D in the disk midplane; vertical forces are neglected.
Test particles: Stars do not interact with each other (no self-gravity, no collisional effects). Each particle samples the background potential.
Units: Positions are in kpc and time in Myr. Velocities use a fixed conversion from km s⁻1 to kpc Myr⁻1.
Axisymmetric background (Eilers et al. 2019): We follow the Milky Way rotation-curve constraints of Eilers et al. and adopt vc(R) that is linear between 5–25 kpc with slope −1.7 km s⁻1 kpc⁻1 and vc(8 kpc)=229 km s⁻1. The radial acceleration is aR=−vc(R)2/R.
Rotating bar (Bovy 2019; cf. Monari et al. 2019): We include a simple rotating quadrupole to mimic the Galactic bar with pattern speed ≈39 km s⁻1 kpc⁻1, present-day angle ≈25°, moderate strength (ε≈0.025), softening ≈0.5 kpc, and an outer taper beyond ≈5 kpc.
Clumpy GMC field (Heyer & Dame 2015; Miville‑Deschênes et al. 2017; Chevance et al. 2020): Giant molecular clouds are represented as softened point masses with a power‑law mass spectrum (β≈1.8), surface‑density–based sizes, random lifetimes with a median 10–40 Myr (varying with radius), and modest velocity dispersion. Clouds appear/disappear to maintain a target count.
Cluster initialization: Stars start within a ~50 pc radius sphere at chosen R, with bulk circular motion plus an isotropic Gaussian velocity dispersion set by the slider.
Integrator: A simple explicit update (Euler/leapfrog-like) advances positions with small time steps tied to the animation frame rate; accuracy favors qualitative behavior over precision.
Boundaries & realism: No live halo, spiral arms, or gas hydrodynamics. Outer radii are limited for stability/visual clarity.
Goal: Provide intuition for how a bar and a clumpy interstellar medium can heat, shear, and dissolve stellar groups over tens to hundreds of Myr.
References (examples): Eilers et al. 2019 (MW rotation curve); Bovy 2019 (bar overview); Monari et al. 2019 (bar pattern speed); Heyer & Dame 2015 (MW GMC review); Miville‑Deschênes et al. 2017 (MW GMC catalog); Chevance et al. 2020 (cloud lifecycle).