When matter is compressed into a single point by gravity, it forms what is known as a singularity. A singularity is a region of space-time where the gravitational field becomes infinitely strong and the laws of physics, as we currently understand them, break down.
The most well-known example of a singularity is found at the center of a black hole. Black holes are formed when massive stars collapse under their own gravitational pull, and if the collapse is sufficiently extreme, a singularity is created at the center. According to our current understanding, the singularity at the center of a black hole is thought to have infinite density and zero volume.
Within the framework of general relativity, the singularity is surrounded by an event horizon, which is the boundary beyond which nothing, including light, can escape the gravitational pull of the black hole. The event horizon is a one-way membrane through which matter and information can only enter the black hole but not escape from it.
At the singularity, the laws of physics as we know them cease to be reliable. The density and curvature of space-time become infinitely large, and our current theories cannot adequately describe what occurs at such extreme conditions. It is believed that a theory of quantum gravity, which combines the principles of quantum mechanics and general relativity, would be necessary to provide a complete understanding of what happens at the singularity.
It's important to note that our understanding of singularities and their properties is based on theoretical models and calculations. While black holes and singularities are predicted by general relativity and have substantial observational evidence supporting their existence, there are still many open questions and ongoing research to better comprehend the nature of singularities and their behavior.