Galaxy Collision Dynamics (2D)

This 2D companion strips the 3D scene down to the physics that actually drives a galaxy merger: the two galactic cores are point masses integrated from real Newtonian gravity (softened so the equations never diverge at close approach), and roughly 1,800 star particles — split evenly between the two disks — respond every step to the combined pull of both cores, the same restricted-three-body technique Alar and Juri Toomre used in 1972 to first reproduce tidal tails numerically. Set a lopsided mass ratio and watch one disk survive almost intact while the lighter one is shredded; set a fast approach or a wide impact parameter and the encounter goes hyperbolic, the cores swinging past each other once and separating for good, with the live "Orbit type" readout confirming it from the actual integrated orbital energy rather than a guess.