Killing horizon

A Killing horizon is a null hypersurface defined by the vanishing of the norm of a Killing vector field (both are named after Wilhelm Killing). A Killing horizon is a null hypersurface defined by the vanishing of the norm of a Killing vector field (both are named after Wilhelm Killing). In Minkowski space-time, in pseudo-Cartesian coordinates ( t , x , y , z ) {displaystyle (t,x,y,z)} with signature ( + , − , − , − ) , {displaystyle (+,-,-,-),} an example of Killing horizon is provided by the Lorentz boost (a Killing vector of the space-time) The square of the norm of V {displaystyle V} is Therefore, V {displaystyle V} is null only on the hyperplanes of equations that, taken together, are the Killing horizons generated by V {displaystyle V} . Associated to a Killing horizon is a geometrical quantity known as surface gravity, κ {displaystyle kappa } . If the surface gravity vanishes, then the Killing horizon is said to be degenerate. Exact black hole metrics such as the Kerr–Newman metric contain Killing horizons which coincide with their ergospheres. For this spacetime, the Killing horizon is located at In the usual coordinates, outside the Killing horizon, the Killing vector field ∂ / ∂ t {displaystyle partial /partial t} is timelike, whilst inside it is spacelike. The temperature of Hawking radiation is related to the surface gravity c 2 κ {displaystyle c^{2}kappa } by T H = ℏ c κ 2 π k B {displaystyle T_{H}={frac {hbar ckappa }{2pi k_{B}}}} with k B {displaystyle k_{B}} the Boltzmann constant. De Sitter space has a Killing horizon at r = 3 / Λ {displaystyle r={sqrt {3/Lambda }}} which emits thermal radiation at temperature T = ( 1 / 2 π ) Λ / 3 {displaystyle T=(1/2pi ){sqrt {Lambda /3}}} .