  Even the elusive neutrinos are trapped in matter, albeit transiently, in
several astrophysical circumstances. Their interactions with the ambient matter
not only reveal the properties of such exotic matter itself, but also shed
light on the fundamental properties of the neutrinos themselves. The physical
sites of interest include the early universe, supernovae, and newly-born
neutron stars. Detection of neutrinos from these vastly different eras using
the new generation of neutrino detectors holds great promise for enhancing our
understanding of neutrino-matter interactions and astrophysical phenomena.
