“Where do astrophysical neutrinos come from?”

Question: “Where do astrophysical neutrinos come from?”
- Keywords:
  neutrinos
Asked by 895furk43 to Sarah, Kieran, Kathryn, Joanne, Chris on 10 Nov 2017.
- Chris Werner answered on 10 Nov 2017:
  
  I remember asking this question myself to my physics teacher in first year and he was astonished I even knew they existed, so brilliant question! There are 3 main types of neutrino, electron, muon and tau. The main type is electron neutrinos and these are produce by fusion reactions in the Sun.
  
  The reaction that takes place which makes up over 80% of electron neutrinos is;
  
  Proton + Proton = Deuterium + positron + electron neutrino.
  
  Deuterium is ‘heavy’ hydrogen’ (symbol D) which is hydrogen with a proton and a neutron, a positron is a positive electron (an anti-electron!). Without the neutrino, energy is lost which can’t happen. Remember the definition that energy cannot be created or destroyed but can be changed from one form to another!
  
  I remember watching a Horizon program which said that there’s close to 100 trillion neutrinos passing through you every second!
- Sarah Guerin answered on 11 Nov 2017:
  
  Yeah Chris is right, the sun produces most of the neutrinos that pass through us- and even though there’s trillions passing through us all the time, scientists have to work extremely hard with very large, advanced and expensive equipment to study them.

Question: “Where do astrophysical neutrinos come from?”