[2] - “Singularities.” Singularities - Black Holes and Wormholes - The Physics of the Universe, https://www.physicsoftheuniverse.com/topics_blackholes_singularities.html.
[3] - “Creation of Black Holes.” Creation of Black Holes - Black Holes and Wormholes - The Physics of the Universe, https://www.physicsoftheuniverse.com/topics_blackholes_blackholes.html.