Structures in the Interstellar Medium Caused by Supernovae: The Local Bubble

Abstract

The Local Bubble is a large low-density region filled with hot gas that surrounds the Sun. The size of the cavity has been determined by absorption line and extinction measurements toward nearby stars and is found to be about 50-200 pc, extending in all directions from the Sun. The fact that the cavity is filled with hot gas has been shown by observations of the diffuse soft X-ray background, which is seen over the whole sky. While there has been substantial progress in understanding the nature of the Local Bubble, limitations in the spectral resolution of the X-ray observations and in models for the origins of the emission, as well as confusion with heliospheric X-ray emission, cause the details of the spatial distribution and ionization state of the hot gas to remain uncertain. Cooler nearby gas such as the Local Interstellar Cloud that surrounds the Solar System provides more clues to the state and origins of the bubble. It appears clear that the bubble was created by multiple supernovae and is now in fairly quiescent state. We review what is known about the bubble and models for its creation.