Black holes are so fascinating because it is where the laws of physics breaks .We have heard a black hole is a infinite dense medium in the universe . Everything that enters a black hole cannot come back . A black hole is actually formed when the fuel(basically hydrogen and helium) of the star burns and it collapses to size zero. We know denisty = mass/volume , and if voulme is zero and density becomes infinte. We can imagine how huge gravitational pull a black hole would have of such great density.Here we have to keep in mind that a black hole will pull the object inside only if it has entered its event horizon.
Black holes are fascinating students as this field has opened a new branch of study ( in quantum mechanics and general relativity) and research.It is fascinating the scientists because black hole is giving us a way to travel in space . Scientists have found out that if somehow a spaceship can travel around a black hole close to the speed of light then the time in that space ship would slow down . Scientists are also finding ways to get back to past( beginning of time ), as if we can travel in future we can also travel in past. May be black holes are the way to our future or will become our end . Either we would travel to some other universe from the black hole or would get eaten up by a huge black hole (assuming billion and billion of years) as we know that a human body gets stretched to pieces inside a black hole . 
Shristi uniyal 