A sub-atomic elementary particle with no electrical charge and very small mass that travels very close to the speed of light. They are created as a result of certain types of radioactive decay or nuclear reaction, such as the decay of a free neutron(i.e. one outside of a nucleus) into a proton and electron. Being electrically neutral and unaffected by the strong nuclear force or the electromagnetic force, neutrinos are able to pass through ordinary matter almost undisturbed and are therefore extremely difficult to detect, although when created in huge numbers they are capable of blowing a star apart in a supernova.