Neutrinos almost don't exist.
They are these hard to detect, ghostly particles that pervade the Universe. A beam of neutrinos could pass through a light year of lead and only one half of them would be absorbed.
Neutrinos have mass but it is estimated to be less than one millionth of the mass of the electron. This means that when they are created they will attain speeds that are very close to the speed of light.
From our own Sun, there are 65 billion neutrinos passing through each square centimeter of your body right now.
During the day they come down from above passing in through your head and out through your feet. At night they come up through the floor in nearly the same numbers because the Earth basically doesn't stop them.
Figure 1. In beta decay of a free neutron decays into a proton and an electron, but wait, there is missing momentum that has gone somewhere?
The neutrino was postulated to exist by Wolfgang Pauli in 1930 to explain how beta decay could conserve energy, momentum, and angular momentum (see Figures 1 and 2). It was actually physically detected for the first time about 26 years later in 1956 .
Figure 2. A free neutron decays into a proton, an electron and a neutrino. Equation balanced. Thank you Dr. Pauli!
So, Who Cares?
Neutrinos are really interesting because they are the only particles that can pass through matter like it does not exist. This means they can be used to explore the center of the Sun, the processes of supernovae and the events that happened within the first few seconds after the Big Bang.
The Sun
The Sun is powered by fusion reactions at its core. From there it takes light up to a million years to reach the surface of the Sun where it can escape into space and warm the Earth and kitties sleeping in windows.
If you are like me you have wondered if this nuclear furnace at the center of the Sun has stopped working?
Rest easy because neutrinos are also created in the same nuclear reaction and pass through the Sun without hesitation. They are detected in vast quantities here on Earth and the numbers add up just fine so we know that the Sun is still working as it should.
Supernovae
Later Ian Shelton announced his observation of a supernova in the Large Magellanic Cloud which produced a massive amount of neutrinos.
Since neutrinos can pass right through a collapsing star like it wasn't there they made it to the Earth before the photons did!
Since then better detectors have enabled researchers to probe deeper into supernova theory and refine their models of these super-powerful events.
The Big Bang
The Big Bang may be the single largest source of neutrinos in our Universe. The first neutrinos were created within the first second after that vent and they fill every cubic centimeter in the Universe.
They form a cosmic neutrino background radiation and the measurement of their energies (temperature distribution gives insight in to that early event).
Closing Words
If neutrinos interacted any less with matter they essentially would not exist. In the universe, there are truly vast numbers of these very strange particles and they are flowing through your body right now. It's weird to think about.
Not much is known about them and research is ongoing. This is good because I think this is good fodder for even more Steemit posts :)
Equations in this post were generated using the Code Cogs online latex editor.