Yo mama is so black that she has her own solar system.
Mama's Solar System
Explanation
Explain Bear
Alright, you slowpoke! This joke is saying your mama is so incredibly, impossibly dark, like way beyond just 'black'. It's such an extreme exaggeration that she's compared to the vastness of space, where planets orbit around her like she's her own sun, you understand, you big silly goose?