Studies of black hole formation from gravitational collapse have revealed
interesting non-linear phenomena at the threshold of black hole formation. In
particular, in 1993 Choptuik studied the collapse of a massless scalar field
with spherical symmetry and found some behaviour, which is quite similar to the
critical phenomena well-known in {\em Statistical Mechanics} and {\em Quantum
Field Theory}. Universality and echoing of the critical solution and power-law
scaling of the black hole masses have given rise to the name {\em Critical
Phenomena in Gravitational Collapse}. Choptuik's results were soon confirmed
both numerically and semi-analytically, and have extended to various other
matter fields.
In this paper, we shall give a brief introduction to this fascinating and
relatively new area, and provides an updated publication list. An analytical
"toy" model of critical collapse is presented, and some current investigations
are given.Comment: 5 figures, revtex. To appear in Braz. J. Phys. (2001
