Does nebula only exist within our galaxy?

No, nebulae do not only exist within our galaxy; they can be found in other galaxies as well. A nebula is a vast cloud of gas and dust in space, and while many well-known nebulae are located in the Milky Way, other galaxies also contain their own nebulae. These interstellar regions can form from various processes, such as star formation or the remnants of dying stars, and are observed throughout the universe.