What astronomical phenomenon did Einstein’s theory help explain?

Einstein’s theory, particularly his General Theory of Relativity, provided significant insights into the nature of gravity and space-time. This theory fundamentally altered the understanding of various astronomical phenomena, most notably black holes.

Black holes are regions in space where the gravitational pull is so intense that nothing, not even light, can escape from them. The existence of black holes was initially theoretical, but Einstein's equations showed that massive celestial bodies could warp space-time to such an extent that they could create these mysterious regions. His theories predicted the occurrence of singularities, which are the core of black holes, where density and gravity become infinite.

The other options do not directly relate to the key contributions of Einstein's theories. The rotation of planets involves Newtonian physics and does not necessarily require Einstein's relativistic framework for basic descriptions, while sunspots and asteroids are phenomena that can be explained without resorting to the complexities of general relativity. Thus, the correct answer centers on how Einstein's theory elucidated the mechanisms behind the existence and behavior of black holes in the universe.