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Three great puzzles

Dark matter

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 eV. 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 :
Didier Verkindt