At http://phys.org/print362921819.html … we have a little history of black holes and how the idea came about. It is illuminating.
This is how a black hole is perceived. In reality all you get is a flash of intense energy.
The idea of black holes is attributed to Sir Roger Penrose, around 50 years ago. The actual idea itself lies beyond the point where physics works, we are told, but he used the theory of relativity to formulate a theorem in which two concepts came together – gravitational singularity (an error in space time) and the idea of trapped surfaces (areas that shrink over time).
Penrose, together with Stephen Hawking, went on describe, mathematically, another theorum, that of the expanding universe (which must have had its origin in another singularity, the Big Bang). The journal Classical and Quantum Gravity (Sept/Oct 2015) has 12 articles highlighting the milestones that mark the 100 year anniversary of Einstein's general theory of relativity – including the one on the Penrose singularity.
At http://phys.org/print362823333.html … astronomers weigh a galaxy's black hole by applying Einstein's 'ring phenomenon' to a far away cluster of stars. Observations of a ring shaped image known as Einstein's Ring (a result of gravitational lensing) was used to calculate a super massive black hole and came up with the impressive figure of 300 millions times the mass of our Sun. The research was published in Astrophysical Research Journal September 28th 2015.