Neutrinos are subatomic and elementary particles, that to say, they can’t be divided into other, smaller particles. Another example of an elementary particle is the electron. Neutrinos were predicted for the first time in 1930, but it wasn’t until 1956 that they were discovered experimentally. Despite its discovery in those dates, scientists continued to think they were massless during many time
Neutrinos are subatomic particles that belong to the family of leptons, and they are the lightest of all the particles that have mass. Even if their mass isn’t known with precision, we know that it is incredibly small: three types of neutrinos have been discovered (with a different mass each of them), and they are so light, that if we add the mass of the three types, they continue to be a million times lighter than one electron. It is thanks to their small mass that they travel through space at a close speed to the one of the light.
In addition, neutrinos are particles without an electric charge. The only way they interact is through gravity and the weak nuclear force, and their interaction with matter is minimal, for which the majority of these particles pass through the Earth and all the other celestial bodies without the least interaction. For this reason they are incredibly difficult to detect and observe.
Abundance in the universe
In the moment of the Big Bang, an enormous quantity of neutrinos was created. Nowadays they are still being produced, in enormous quantities. These particles are mainly produced at the nuclei of stars, due to nuclear fusion, in particle accelerators, in the explosions of supernovae, in black holes, in quasars… It is estimated that in the universe there are a billion times more neutrinos than protons. But, despite their ubiquity, neutrinos remain to be a big mystery to scientists, as they are very complicated to detect.
These particles are so abundant and their interactions with matter so small, that every second hundreds of trillions of neutrinos pass through our body without us feeling them. Their abundance is only surpassed by the number of photons (the particles of light) that exist in the universe.
Their detection, an activity that requires a lot of patience
The study of neutrinos is very complicated, as their minimal interaction with matter makes them very difficult to detect. It is for this reason that, to try to increase the odds of detecting them, scientists build huge detectors and create intense sources of neutrinos. Normally these detectors are situated underground, to isolate them from cosmic rays and other background radiations.
Being so small and neutral, these particles can’t be detected directly. All the techniques used nowadays for the detection of neutrinos rely on detecting the electrically charged and heavier particles that are created when a neutrino interacts with the atoms of different materials in the detector, creating indicators of this event (changes in temperatures, flashes of light…).