Three great puzzles
Since more than 20 years, a strange puzzle gives headaches to astrophysicists.
Measurements of the
orbital velocity of stars in many galaxies give unexpected results.
The outer stars of galaxies are orbiting
more rapidly than expected.
Gravitation has been doubted and an hypothetical fifth force was invented... but nothing
was able to give a simple explanation to those too high velocities.
An other explanation is that some dark matter, invisible, is orbiting around and
inside the galaxies, only detectable through its gravitational effects.
If neutrinos were massive, they would be good candidates
to this dark matter, since the theory says that they must be numerous in the universe:
330 neutrinos per cm3.
A good candidate, but with the condition that its mass is neither
too small nor to high.
The missing solar neutrinos
Since 1975, and especially since 1995, physicists know with assurance that the neutrinos
coming from our sun are largely less than predicted.
The theory, which elsewhere describes with an accurate precision how the sun lives,
predicts about 64 billions of neutrinos per second and cm2, received on earth.
Detectors like GALLEX or SAGE
observe not more than 40 billions of neutrinos per second and cm2.
Where are the missing neutrinos?...
Either the model describing the sun, so remarkable, is erroneous, either something
makes the neutrinos impossible to arrive on the earth of impossible to detect.
If the neutrinos have a mass, then they could oscillate and those oscillations could
explain the missing solar neutrinos.
Very high energy cosmic rays
Since about 30 years, a phenomena, whose origin is still unknown and which is called
"cosmic rays", keeps a mystery. The cosmic rays of high energy are particles coming from
somewhere in the universe and producing a great shower of particles
(pions, kaons, muons, electrons, neutrinos, photons...) when collisionnin
with the atoms of our atmosphere.
Some of those cosmic rays have been detected
and it was found that they have more energy than
an ace tennis ball, that is about 10 Joules, that means about 1020
This is a lot of energy for only one particle. If the particle were a tennis ball, it would
have an energy of 1046 eV, that is 1027 Joules. This is about 10 times
the energy released by the whole sun each second. For now, no known
cosmic phenomena is able to accelerate a particle to reach such energy.
Some physicists think
that those high energy cosmic particles could be neutrinos.
But from where and how do they acquire such an energy?
Mystery is still open.
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Last update: 26/06/1999 : http://wwwlapp.in2p3.fr/neutrinos/anenigmes.html