A superbubble is a cavity hundreds of light-years across filled with hot, low-density gas, blown into the interstellar medium by multiple supernovae and stellar winds from massive stars. Our solar system is currently traveling through one known as the Local Bubble.
The Local Bubble is a cavity in the interstellar medium roughly 300 light-years across. It contains hot, diffuse gas and is thought to have been carved out by multiple supernovae millions of years ago.