I’ve seen it suggested that the hypothetical planet Nine could be a black hole five to 10 times the mass of Earth. As I understood it, however, the minimum weight of a black hole is 3 solar masses, so how could the Planet be a black hole?
William Jennings
Eugene, Oregon
Typically, black holes fall into one of three categories: stellar-mass, intermediate-mass, or supermassive. The lower limit for a stellar-mass black hole is still unclear. When a large star goes supernova, it leaves beh