One approach for gaining all this knowledge is to pick a couple of good introductory books on general relativity or black holes and leave it at that. I, on the other hand, prefer to go a step further. I like to go way back to original papers.
In almost every distinct scientific field, there is one or more seminal paper that launches a successful new idea or significant direction. In my example above, Einstein’s original papers from the early 1900’s are a great example. I’ve gone back to read these papers to get a more solid foundation for the more contemporary theories. I find that it helps to read the research that started it all. I’ve done the same in other fields, like reading the original Watson and Crick paper from 1953 proposing the double helix structure of DNA. One of my favorites in the field of cosmology is Edwin Hubble’s original paper “A Relation Between Distance and Radial Velocity Among Extra-Galactic Nebulae” from 1929 and Hubble’s book “The Realm of the Nebulae” from 1936. Hubble’s original work changed cosmology forever after his observations led to the realization that the universe is expanding.
The only problem with seeking out original papers is they may be hard to find. Even with the Internet where scientific research is so readily available, finding original papers may be a challenge. The reason of course is that in early days, papers were in print form only. Old papers would need to be digitized and converted to commonly accepted formats such as Postscript and PDF, or even graphic file formats such as JPEG. This isn’t always the case. Nevertheless, I’ve found that with fortitude, I’m usually able to find most original papers eventually.
The acquisition of original papers may be extra work, but I think it is well worth while in order to get a good foundation for your favorite areas of study, plus the detective work needed to locate them can be fun.