  Astronomical observations in the electromagnetic window - microwave, radio
and optical - have revealed that most of the Universe is dark. The only reason
we know that dark matter exists is because of its gravitational influence on
luminous matter. It is plausible that a small fraction of that dark matter is
clumped, and strongly gravitating. Such systems are potential sources of
gravitational radiation that can be observed with a world-wide network of
gravitational wave antennas. Electromagnetic astronomy has also revealed
objects and phenomena - supernovae, neutron stars, black holes and the big bang
- that are without doubt extremely strong emitters of the radiation targeted by
the gravitational wave interferometric and resonant bar detectors. In this talk
I will highlight why gravitational waves arise in Einstein's theory, how they
interact with matter, what the chief astronomical sources of the radiation are,
and in which way by observing them we can gain a better understanding of the
dark and dense Universe.
