Stars have a magnetic field and rotate along their axis, similar to planets. The burst is emitted along the axis of rotation (the geographic north and south pol

Stars have a magnetic field and rotate along their axis, similar to planets. The burst is emitted along the axis of rotation (the geographic north and south pole). Many stellar objects rotate and/or have a magnetic field, and thus an "up", "down", and "side" in spite of being a sphere. Pulsars (extinguished stars that emit radio waves from their poles) are another famous example.