According to our current understanding of black holes in the framework of general relativity, black holes are regions of spacetime with extremely strong gravitational forces from which nothing, not even light, can escape. They are formed when massive stars collapse under their own gravity.
As for the possibility of a black hole turning into something else as it becomes more massive, it's important to clarify a few points.
First, black holes themselves do not undergo any physical transformation or change. They are characterized by their mass, charge, and angular momentum, which are conserved properties. A black hole remains a black hole as long as its event horizon—the boundary beyond which nothing can escape—persists.
However, there is a concept called black hole evaporation, proposed by physicist Stephen Hawking, which suggests that black holes can slowly lose mass over an extremely long timescale due to quantum effects. This phenomenon is known as Hawking radiation. According to this theory, black holes emit particles and radiation over time, causing them to gradually lose mass and energy. As a black hole loses mass through Hawking radiation, its temperature increases, and eventually, it may evaporate completely.
If a black hole were to lose enough mass through Hawking radiation, it would eventually reach a point where its energy and curvature of spacetime are no longer sufficient to sustain an event horizon. At that stage, it would cease to be a black hole. However, the process of black hole evaporation is incredibly slow, and for all practical purposes, it is not currently observable or relevant for astrophysical black holes in our universe.
It's worth noting that our current understanding of black holes and their behavior is based on general relativity and quantum field theory. The reconciliation of these theories into a complete theory of quantum gravity is an area of ongoing research and could potentially lead to new insights and revisions to our understanding of black holes in the future.