Black Holes: Cosmic Mysteries and Unsolved Physics

This comprehensive report, updated to mid-2025, offers a detailed overview of black hole physics. It begins by explaining the theoretical framework of black holes, rooted in Einstein's general relativity, including concepts like the event horizon and singularity, and the "no-hair" theorem. The text then describes the anatomy and different classifications of black holes—stellar-mass, supermassive, intermediate-mass, and primordial—along with their formation and observable features like accretion disks and relativistic jets. It further details the observational evidence confirming black holes, such as stellar orbits, gravitational lensing, gravitational waves, and direct imaging from the Event Horizon Telescope, highlighting recent discoveries. Finally, the report addresses unsolved problems like the information paradox and the ongoing quest for a quantum gravity theory, also exploring the intriguing possibility of primordial black holes as dark matter, demonstrating their continued importance as theoretical laboratories for fundamental physics.