Horizons in 2+1-dimensional collapse of particles

DIETER BRILL¹, PUNEET KHETARPAL² and VIJAY KAUL¹

¹Department of Physics, University of Maryland, College Park, MD 20782, USA

²Rensselaer Polytechnic Institute, Troy, NY 12180, USA

E-mail: brill@physics.umd.edu

Abstract. A simple, geometrical construction is given for

three-dimensional spacetimes with negative cosmological constant that

contain two particles colliding head-on. Depending on parameters like particle

masses and distance, the combined geometry will be that of a particle, or of

a black hole. In the black hole case the horizon is calculated. It is

found that the horizon typically starts at a point and spreads into a

closed curve with corners, which propagate along spacelike caustics and disappear

as the horizon passes the particles.

Keywords. Black holes; gravitational collapse; horizon.

PACS Nos 04.20.Gz; 04.60.Kz; 04.70.Bw