Warm hydrogen gas is a major component of our Galaxy. However, it is peppered with holes. This image from the Australia Telescope Compact Array and the Parkes radio telescope shows one such hole, called GSH 277+00+36. This void is more than 2000 light-years across, and was probably formed by winds and supernova explosions from about 300 massive stars. Over the course of several million years, the hole expanded and eventually grew so large that it broke through the disk of the Galaxy.
Credit: ATCA and Parkes image in HI by N. McClure-Griffiths and the Southern Galactic Plane Survey team.
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