- https://science.nasa.gov/astrophysics/focus-areas/black-holes
- https://en.wikipedia.org/wiki/Black_hole
- https://astrosociety.org/edu/publications/tnl/24/24.html
- http://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-black-hole-58.html
- http://www.sciencealert.com/watch-the-life-and-death-of-black-holes-explained
- http://www.space.com/20881-wormholes.html
- http://fermi.sonoma.edu/teachers/blackholes/BFfactsheet09wide.pdf