According to Albert Einstein time is a dimension and it is moving continuously in uni direction at a constant speed. If we need to change its speed we have two ways such that be move at higher velocities , since the time is our physical dimension ,when we move actually we are making a change in the constant velocity of time (a small change). If we move at the speed of light we could stop the time, if we overtake the speed of light then we may be possible to travel back in time but, mass can’t reach or overcome the velocity of light so time traveling using velocity is not possible for any living beings .
But special relativity says that space consists of time so if space is bent, time is also bent. Then we must consider what bents the space; mass does. Mass makes bents and distortions in space as well as time . This means that if we are standing near a massive body which curves the space as well as time then our time runs at low speed. Then there will be a point at which the time stops, at that point the mass around it will be so huge. Even a light ray can’t escape form it since it’s escape velocity is more than the speed of light.
if the light don’t nothing can escape it , yes it is the black hole. The black holes are actually a bridge between 2 time levels when we fall into a black hole then we are actually doing time travel. As we approach the center of black hole more and more we go back in time. There may be a future in which we can depend upon artificial and limited black holes to go back into a specific time and to change the past!!!