black hole

Region in space where a sufficient amount of mass is concentrated so that it forms a gravitational prison – a region into which matter or light can enter from the outside, but from which nothing that has once entered can ever leave.

Basic information on this key phenomenon of Einstein’s general theory of relativity can be found in the chapter Black holes & Co. of Elementary Einstein.

Selected aspects of the physics of black holes and neutron stars are described in the category Black holes & Co. of our Spotlights on relativity.

In Einstein’s theory, black holes are truly black, due to the fact that no radiation or light can ever escape them. Once quantum theory is taken into account, this assumption no longer holds – on the contrary, it seems as if black holes should emit so-called Hawking radiation. However, for astrophysical black holes (that typically have more or even much more than one solar mass), that radiation would be undetectable, even if we could transport today’s most sensitive sensors into the immediate vicinity of the black hole.