  We review an optimal-filter-based algorithm for detecting candidate sources
of unknown and differing size embedded in a stochastic background, and its
application to detecting candidate cosmic bubble collision signatures in
Wilkinson Microwave Anisotropy Probe (WMAP) 7-year observations. The algorithm
provides an enhancement in sensitivity over previous methods by a factor of
approximately two. Moreover, it is optimal in the sense that no other
filter-based approach can provide a superior enhancement of these signatures.
Applying this algorithm to WMAP 7-year observations, eight new candidate bubble
collision signatures are detected for follow-up analysis.
