Schematic of a wind-blown bubble inside a galactic magnetic field. As the bubble expands it compresses the magnetic field lines (black lines), which increases the local magnetic pressure. The expansion of the outer shell (solid red line) stops when the thermal pressure (p_T), which drives the expansion is equal to the external magnetic field pressure P_B. This determines the location of the wind termination shock (dashed red line), which is located at the point where the ram pressure of the wind (p_ram) is equal to p_T.