# Black Holes

${\displaystyle {\textrm {d}}s^{2}=-(1-{\frac {GM}{r}}){\textrm {d}}t^{2}+{\frac {{\textrm {d}}r^{2}}{1-{\frac {GM}{r}}}}+r^{2}{\textrm {d}}\Omega ^{2}}$
which goes wrong when ${\displaystyle r\rightarrow GM}$. This point is called the "horizon" of the black hole. At this point (where r is measured from the black hole) the metric becomes all space-only and the time coordinate is killed. This is the Schwarzschild Black Hole, invented by Arnold Schwarzschild after 1915. Other Black Holes were later invected that hide charge and can spin, and can even be "extended" by black branes.