Black holes lurk, mysteries abound.

Meaning: Black holes are mysterious objects in space that are difficult to understand and there are many unanswered questions about them.

Choice of Words: Black holes are regions of spacetime where gravity is so strong that nothing, not even light, can escape, while mysteries are things that are difficult or impossible to understand. Lurk means to lie in wait for someone or something, while abound means to be present in large numbers.