The two correct answers for identifying a planetary nebula are:
1. **Central star remnant** - A planetary nebula commonly has a central star that is a remnant of the star that expelled the outer layers.
2. **Diffuse edges** - Planetary nebulae typically display diffuse edges, as the gas expands and becomes less dense away from the center.
So, the correct responses are "central star remnant" and "diffuse edges."