Linked from
The 62 pages that link to Black hole, each with the reason it gives.
X-ray astronomyRelated: X-rays from surrounding hot gas trace matter falling toward black holes.
Stellar massRelated: If a collapsing remnant is massive enough, it can form a black hole.
Light coneRelated: Inside its event horizon, future-directed light cones point inward.
Causal structureRelated: Its defining boundary is a feature of global causal structure.
UhuruRelated: Uhuru data strengthened the case that some bright X-ray binaries contain black holes.