The shape of the bubble for simulation F after 4.45, 4.5, 4.55, and 4.6 Myr. During the red supergiant phase (left panel), the hot, shocked wind bubble is destroyed completely by the combined forces of the interstellar magnetic field and the thermal pressure in the ISM. The result is a purely radiative collision between the red supergiant wind and the outer shell (left side of left panel.) Once the start reaches the Wolf-Rayet stage (right side, left panel), the powerful wind quickly sweeps up the red supergiant wind, forming a new hot bubble that starts to expand into the ISM (right panel).