Ask A Scientist© Astronomy Archive

Question:  What exactly are neutrino's and why are they important?!?!?
Saundra

Answer 1:  The existence of neutrinos was postulated to explain what was
observed when a nucleus undergoes beta decay via electron emission (a neutron in 
the nucleus changes into a proton, and the nucleus emits an electron).
Observation seemed to indicate that, in general, neither momentum nor total ener gy was conserved in such a
reaction. This was, understandably, disturbing. In 1931 the physicist Pauli
proposed that another, unseen particle was also being emitted in the reaction,
accounting for the "missing" momentum and mass-energy. Fermi named this particle  "neutrino" meaning
"little neutral one". The name reflected the assumption that it had no electric
charge (so that the law of charge conservation would remain intact);
additionally, it was postulated to have zero spin (keeping the law of conservati on of angular momentum) and to
interact only weakly with matter (to explain why it was virtually undetectable). 
Eventually the neutrino was detected, in the early 1950's, through nuclear
reactors (which produce huge numbers of neutrinos). Currently it is believed tha t there are three
kinds of neutrinos (plus their antiparticles, making a total of six) -- the
electron-neutrino, the muon-neutrino, and the tau-neutrino. Neutrinos are
considered to be the force-carriers associated with the fundamental force called  the weak force. The weak
force is very important -- it contributes to the production of elements of
higher atomic number, without which life as we know it would be impossible.
Rcwinther

Answer 2:  And they're important in astronomy for several reasons:
supernovas emit huge quantities of neutrinos (according
to theory).  Supernovea 1989A, which was nearby in one of the
Magellanic clouds, was detected by several neutrino detectors
that had been designed and built to detect neutrinos from the
sun:  the best theories of how the sun works predict three times
the number of neutrinos than are actually detected!
Neutrinos may play a major role in the dark or missing matter
problem of cosmology.
john (e-mail hawley)