Still Hawking has a point. A black hole is a gravitional center so strong that once something enters,then nothing not even light can escape. Never understood what the source of a such a gravitational field could be and since there is inherent energy associated with mass what happens to all that energy when mass is absorbed by a “black hole”.
Not quite. They actually evaporate over time.
Never understood what the source of a such a gravitational field could be
The source of the field is a collapsed star or other object with mass greater than the Chandrasekhar Limit. Such an object collapses under its own mass. In General Relativity, this collapse is down to a single point, called "the singularity." We do not have a Quantum Theory of Gravity, but all bets -- and mathematical estimates based on QFT and/or the Uncertainty principle -- are that in the Quantum version, the mass cannot quite collapse to a single point.
what happens to all that energy when mass is absorbed by a “black hole”
Nothing happens to it. It's still there inside the hole. Because the hole is not a "hole," it's a region of space near the singularity. In the early 20th century, it was known these kinds of masses could theoretically exist; so massive that light could not escape. At that time they were called "frozen stars" to capture the idea that light could not escape them. Black Hole is better but still leaves room for misinterpretation. There is no hole. It looks like a "hole" to an outside observer, because things that get close enough (even light) "fall in." A better term might be Black Suckers or Black Gobblers.