Black holes
In astronomy, black holes are regions of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole.
Artists impression of a black hole with an associated magnetic field. image: NASA
The boundary of the region from which no escape is possible is called the event horizon. Although crossing the event horizon has enormous effect on the fate of the object crossing it, it appears to have no locally detectable features.
The supermassive black hole inside the core of the supergiant elliptical galaxy Messier 87 in the constellation Virgo. Its mass, estimated at 7.22+0.34 −0.40×109 M☉, is billions of times that of the Sun. It was the first black hole to be directly imaged by the Event Horizon Telescope