The Geminga supernova as a possible cause of the local interstellar bubble

THE Solar System resides at the edge of a cavity of hot (10⁶ K), low-density (5×10^-3 cm^-3), X-ray emitting gas embedded in the interstellar medium^1-4. This void, sometimes called the Local Bubble, is thought to be less than 10⁷ years old, but its origin is unknown. Here we propose that the void was caused by the supernova that produced the Geminga pulsar. The initial identification⁵ of Geminga as a pulsar, and the subsequent detection^6-8 of pulsations in high-energy γ-rays, give an age of 3×10⁵ years and a pulsar distance in the range 40 to 400 pc (refs 6,7). Using this information, and the recently discovered^9,10 proper motion of a likely optical counterpart, we find that the supernova was well positioned to produce the local void, provided that the explosion occurred within about 60 pc of the Solar System. Larger distances are not excluded by our analysis, but they would put the supernova at a position for which there is no evidence for such an energy input.