Assertion: black hole | /r/HasProperty | compact
Facets:
Source sentences:
text: Hence, observation of this mode confirms the presence of a photon sphere, however it cannot exclude possible exotic alternatives to black holes that are compact enough to have a photon sphere.
text: Though black holes are compact objects, they are exceptionally massive — the mass of M87's black hole is about 6.5 billion times that of our sun, the National Science Foundation (NSF) said in a statement.
text: Because they are so compact, they have very strong gravity.