Interaction of the Loop I Supershell with the Local Hot Bubble

A soft X-ray shadow has been discovered on the periphery of the Loop I supershell in the ROSAT All Sky Survey. The distance, size, geometry and spectral data indicate that it is cast by an annular volume of dense neutral matter which has formed in the collision of the Loop I superbubble and the Local Hot Bubble. This is the first observation of the interaction region of two colliding interstellar bubbles, and the results are consistent with earlier theoretical work on colliding spherical shock waves.