I am back again with particles post. I was thinking if first should be about electrons or photons and then I realized that neutrinos are kind of really special and fun so I will start with them.
Neutrinos are small particles in group called leptons.
They can be created by thermonuclear reaction which is happening in stars so there are huge amounts of them flying in the Universe. Actually there is so much of them that every second millions of them will pass through every cm^2 of your body. Before it was thought that they are massless which would mean that they are able to travel at the spead of light which is not true, they have some mass but it is not much.
It is really hard to detect them but there are machines that can do that. I think that one of them is built under ice in the Antarctic continent. Even when there is so many neutrinos it can detect only extremely small fraction of them (I would not try to quess the numbers).
Neutrinos also dont interact very much so they are able to pass through whole earth without slowing down.
Supernovas are also really great source of neutrinos but they do not occur that often.
On the Earth we create it in nuclear reactors and neutrinos are also made inside the Earth because as I said in some previous post when material is beta decaying it will release neutrinos.
In the year of 2011 there was mistake when measuring the speed of neutrinos. Computer counted that traveling neutrino was able to travel distance 60 nanoseconds faster than light which is not possible. Soon they luckily knew where was the mistake.