According to conventional astronomical wisdom, the sun sits in a bubble of million-degree hydrogen gas, which is itself enclosed by colder, denser gas. The new observations, however, reveal that the sun resides in what might be better described as a tube or chimney of low-density gas that has a spongelike network of cavities and tunnels linking it to other low-density pockets beyond the dense gas wall. These nooks and pathways, Barry Welsh of the University of California at Berkeley and his collaborators suggest, may have been scoured out by supernovas or powerful stellar winds.
This new view of the sun's environs fits neatly with a model of the Milky Way first proposed nearly three decades ago, in which supernova explosions create interconnected tunnels of hot gas in the space between the stars throughout the galaxy.
Looking forward, the team hopes to glean further details about the motion of the atoms making up the dense gas enclosure. "Soon we will be able to say whether the gas wall that surrounds our local void is coming towards the sun and squeezing our local interstellar space, or whether it is moving away from us such that the local void is getting larger," Welsh remarks. "Either of these scenarios is fascinating. If the wall is approaching us, it means that a distant explosive force is pushing it towards us. If it is expanding away from the sun, then it seems possible that a supernova explosion took place about a million years ago that was located relatively close to our sun."