The Large Magellanic Cloud (LMC) isn’t what it seems. Yes, it looks like a rotating galaxy, but the stars inside tell a different story. While gas moves with a velocity gradient (60–100 km/s), stars show no rotation. Why?
N-body hydrodynamical simulations show that the SMC-LMC collision occurred about 100 million years ago, transforming the SMC’s internal structure. The gas, struck by the LMC’s disk, received a ~30 km/s kick, destroying rotation and shifting the stellar center relative to the gas center. Stars developed a dispersion-dominated kinematics (v/σ ≈ 0.2), with radial outward motions beyond R > 2 kpc. This explains the large line-of-sight depth (~10 kpc) and the offset between photometric and kinematic centers. The collision also generated a tidal tail contributing to the SMC’s extended structure. These findings suggest group interactions are key in transforming irregular galaxies (dIrr) into elliptical or dwarf spheroidal galaxies (dE/dSph), removing gas and altering structure. Modeling the SMC as a transitioning galaxy is essential for correctly interpreting observational data regarding interstellar medium and dark matter physics.
