Editing Skein of Worlds:The Material Plane (section)

=== The Negative Energy Spheres ===
The negative energy spheres, or black holes, are very similar to suns. They're about the same size, and don't have much of a surface or native life. The biggest difference is that a black hole is a vortex to the negative energy plane. Since it neither emits nor reflects light, it's very difficult to see, unless it's close enough to block the light from something else, such as a number of stars or a sun or planet.

A planet too close to a black hole would be a very dark place. Even during the day, it wouldn't be as bright, and at night the black hole could be seen as a great black disk in the sky. Any native life on such a planet would tend to grow and reproduce fairly slowly.