Whence the Local Bubble, Gum, Orion? GSH 238+00+09, A Nearby Major Superbubble toward Galactic Longitude 238o

We examine H I, IR, radio continuum, and 1/4 keV X-ray data and find evidence for a nearby (~0.8 kpc) superbubble in all four data sets. GSH 238+00+09 follows the official IAU naming convention and specifies the central Galactic coordinates and the LSR velocity. Its mass and energy required for production rank it among the major supershells in the Galaxy. It is at least partially responsible for the apparent extreme elongation of the Local Bubble toward ℓ~230°, and it might intersect the Local Bubble or the Lindblad Ring. It cleared out a large cavity into which the Eridanus Loop and the Gum Nebula currently expand, and it may have been responsible for shock-induced star formation in the Gum, Orion, and Mon R2 regions. There are several candidates for the originating star cluster of GSH 238+00+09, of which the most interesting is Collinder 121.