Describe the formation of black holes and their properties as predicted by general relativity. How does the event horizon define a black hole?
The correct answer and explanation is:
A black hole forms when a massive star undergoes gravitational collapse, typically after exhausting its nuclear fuel. According to general relativity, when the core of a star can no longer support itself against the force of gravity, it collapses into an infinitely dense point known as a singularity. The gravitational pull around this singularity becomes so intense that not even light can escape, resulting in what we call a black hole.
The key feature of a black hole is its event horizon, which is the boundary beyond which nothing, not even light, can escape its gravitational grip. The event horizon is not a physical surface but a mathematical concept that marks the point at which the escape velocity equals the speed of light. Once something crosses the event horizon, it is effectively trapped inside the black hole. The escape velocity inside the event horizon exceeds the speed of light, making it impossible for any information or matter to escape back into the observable universe.
The properties of a black hole, as described by general relativity, include the mass of the black hole, its spin (or angular momentum), and its charge (if any). These characteristics determine the nature of the black hole’s gravitational field and how it interacts with its surroundings. A black hole’s gravitational influence is governed by the equations of general relativity, where spacetime is warped severely near the event horizon. This warping results in extreme gravitational time dilation, where time appears to slow down as an object approaches the event horizon.
The singularity itself, located at the center of a black hole, is a point where the curvature of spacetime becomes infinite, and our current understanding of physics breaks down. However, this theoretical prediction remains unproven due to the inability to observe the interior of black holes directly.