A cosmic bubble is an astronomical object consisting of a hot gas that is surrounded by a cooler shell of gas. The word “bubble” can be used to refer to either the entire object, or just the hot gas interior. Cosmic bubbles are thought to be formed by the interaction of powerful astrophysical phenomena, such as supernovae, with their environment.
Bubbles have been observed in a variety of objects, including galaxies, star clusters, and nebulae. In our own Milky Way galaxy, several dozen bubbles have been identified. The best-known example is the Bubble Nebula (NGC 7635), which was created by the shock wave from a supernova explosion that occurred about 10,000 years ago.
Cosmic bubbles are often classified according to their shape. Round bubbles are called “shells”, while elongated ones are referred to as “chimneys”. Some objects show evidence for both types of structures. It is believed that different shapes are created by different formation mechanisms. For example, round shells may be produced when a shock wave expands outward from a central point; chimneys may form when material flows out along lines of least resistance in an inhomogeneous medium.
Most cosmic bubbles appear to be relatively young objects, although some may be quite old (up to a few hundred million years). This is likely due to the fact that they are destroyed or disrupted over time by various processes, such as interactions with other bubbles or with dense clouds of interstellar gas and dust. Nevertheless, Bubbles provide us with important clues about some of the most energetic events in the Universe