  Dwarf galaxies have attracted increased attention in recent years, because of
their susceptibility to galaxy transformation processes within rich galaxy
clusters. Direct evidence for these processes, however, has been difficult to
obtain, with a small number of diffuse light trails and intra-cluster stars
being the only signs of galaxy disruption. Furthermore, our current knowledge
of dwarf galaxy populations may be very incomplete, because traditional galaxy
surveys are insensitive to extremely diffuse or compact galaxies. Aware of
these concerns, we recently undertook an all-object survey of the Fornax galaxy
cluster. This revealed a new population of compact members, overlooked in
previous conventional surveys. Here we demonstrate that these 'ultra-compact'
dwarf galaxies are structurally and dynamically distinct from both globular
star clusters and known types of dwarf galaxy, and thus represent a new class
of dwarf galaxy. Our data are consistent with the interpretation that these are
the remnant nuclei of disrupted dwarf galaxies, making them an easily observed
tracer of galaxy disruption.
