  Some years ago it was shown that the cosmological constant may be reduced by
thermal production of membranes that, after nucleation, collapse into a black
hole. The probability of the process was calculated in the leading
semiclassical approximation by studying an associated Euclidean configuration
called the thermalon. Here we investigate the thermalon in three spacetime
dimensions, describing the nucleation of closed strings that collapse into
point particle singularities. In this context we may analyze the one-loop
structure without the well known problems brought in by the propagating
gravitational degrees of freedom. We found that the coupling to gravity may
increase the number of negative eigenvalues of the operator.
