Local Bubble

The Local Bubble is a cavity in the interstellar medium (ISM) in the Orion Arm of the Milky Way which contains the Local Interstellar Cloud and G-cloud (as well as others). It is at least 300 light years across and has a neutral hydrogen density of about 0.05 atoms per cubic centimetre, or approximately one tenth of the average for the ISM in the Milky Way (0.5 atoms/cc), and one sixth of the Local Fluff, or Local Interstellar Cloud (0.3 atoms/cc). The hot diffuse gas in the Local Bubble emits X-rays.

The very sparse, hot gas of the Local Bubble is the result of supernovae that exploded within the past ten to twenty million years. It was once thought that the most likely candidate for the remains of this supernova was Geminga ("Gemini gamma-ray source"), a pulsar in the constellation Gemini. More recently, however, it has been suggested that multiple supernovae in subgroup B1 of the Pleiades moving group were more likely responsible.