  Multi-Conjugate Adaptive Optics (MCAO) combines the advantages of standard
adaptive optics, which provides high contrast and high spatial resolution, and
of wide field ~1' imaging. Up to recently, MCAO for astronomy was limited to
laboratory experiments. In this paper, we present the first scientific results
obtained with the first MCAO instrument put on the sky. We present a new study
of the Trapezium cluster using deep MCAO images with a field of view of 1'x1'
obtained at the VLT. We have used deep J, H and Ks images recently obtained
with the prototype MCAO facility MAD at the VLT in order to search for new
members and new multiple systems in the Trapezium cluster. On bright targets
(Ks~9mag), these images allow us to reach DeltaKs~6mag as close as 0.4" We
report the detection of 128 sources, including 10 new faint objects in the
magnitude range between 16.1<Ks<17.9mag. In addition to all previously known
multiple systems with separations greater than 0.1", we confirm the
multiplicity of TCC-055. We also report the detection in J, H and Ks of a very
red extended embedded protostellar object, HC419, previously detected in the
thermal infrared only. The analysis of the first MCAO images obtained on the
sky demonstrates not only the technical feasibility of MCAO but also its great
potential and versatility in terms of scientific outputs.
