Black hole creation in 2+1 dimensions

When two point particles, coupled to three-dimensional gravity with a negative cosmological constant, approach each other with a sufficiently large centre-of-mass energy, then a BTZ black hole is created. An explicit solution to the Einstein equations is presented, describing the collapse of two massless particles into a non-rotating black hole. Some general arguments imply that massive particles can be used as well, and the creation of a rotating black hole is also possible.