The surface of the sun is hot, but even more so, at its core is a crazy intense pressing together of  hydrogen atoms, that pressing called nuclear fusion.  

Like being deep underwater, when your ears pop from the added pressure, the huge sun presses down at the core, sparking radiative processes that chase photons and neutrinos outwards.

The photons struggle to get back to the surface, but the neutrinos zing out.

If you were to point at the sun while reading this, even if at night, when people in China are enjoying daylight, the number of neutrinos coming from the sun and going through the tip of your pointing finger, is immense; trillions every passing second, that’s a 1 followed by 12 zeros, or one thousand billion neutrinos.

Fusing hydrogen together spawns neutrinos, in that case neutrinos which are kin to electrons, as both are produced in that fusion process.

Our Sun is the mother of a solar system of eight planets, and a couple dwarf planets. Each and every star out there is some solar system’s sun. Each is fired by the same fusion process that produces neutrinos, their sister electrons, and both visible and invisible light.

There are hundreds of billions of suns in the Milky Way galaxy, maybe thousands, and a similar number in our nearest neighbor, Andromeda.

Wow, so many neutrinos are zinging around the galaxy, should we learn more, and study these birds?

Other particles are produced in deep space, protons for example also are chasing around, some of which find their way to the Earth, sort of like flashing shooting stars, penetrate the highest reaches of the Earth’s atmosphere and bump into the nitrogen and oxygen that eventually we breathe.

These cosmic protons, like the solar-born neutrinos, are moving fast, very fast, and therefore pack a punch; consider that speed to be 186,000 miles per second – woh! That’s the same as the speed of light.

Protons are very light weight, as well as being tiny in size. Too tiny to see with microscopes of any kind, although with modern technology seeing molecules is nearly possible. In your body there are approximately one trillion trillion protons – cool.

Despite their fast speed and small size, these Earthbound protons have a lot of energy – like imagine how good you feel when you sleep well, and are excited about the coming day, lots of capacity to do things, lots of energy.

With that high energy, the incoming protons shake up the nitrogen and oxygen they fly by, high altitude interactions fired by their electrical and magnetic natures; the result is that a different particle is born, these are called pions.

Electrons are easy to make because they are among the smallest of particles, as are pions. In collisions of subatomic particles, for example protons on protons, pions become commonplace.

Pions being bigger than electrons, think mass, not size, their tendency is to exhaust themselves and become an electron. Sort of like if a marble were released from the rim of a large bowl which sets on a tabletop, in short order it’d naturally find itself at the bowl’s center, and motionless, its energy zapped. It turns out that pions becoming electrons is a multistep process but occurs in a flash of time, very quickly.

Charged pions traveling in mostly the same direction as its parent proton was, become “massive electrons” and neutrinos. This process is called decay, in this case pion decay, but what are massive electrons?

Well these massive particles are in every way the same as electrons, but more massive; think of them as overweight electrons, and we call these electron-like overweight particles muons.

That is, Earth-bound cosmic protons interact with nitrogen up above where jet airliners fly, produce muons, and then decay into electrons and neutrinos.  These types of neutrinos are deemed muon-type neutrinos, as they are spawned from muons. And yes, the neutrinos that emanate from the sun are electron-type neutrinos.

Albeit much much more rarely, muon-type neutrinos interact with matter (the denser the better) to produce muons, and electron-type neutrinos produce electrons, each with a characteristic signature.

So nature provides us with interesting phenomena, neutrinos have types, physicists call those neutrino flavors.

And finally, nature allows for “obese electrons,” but we will be nice and call those tau-ons, and the corresponding neutrinos are then, tau-type neutrinos. These are mighty but rare, seldom “seen” particles.

Summarizing: that’s three neutrino flavors: electron, muon, and tau-type neutrinos. And I trust this dialog has helped with your question on neutrinos.

There is a great amount of history to learn that goes back almost one hundred  years when neutrinos were first postulated (thought to exist), but no one had “seen” one until the 1950’s (election-type), the 1960’s (muon-type), and in 2000 (tau-type).

Experimentalists like myself are interested in learning more about what neutrinos are, and how they do what they do.

At Fermilab National Accelerator Laboratory, near Chicago, sometimes called Fermilab and named after Enrico Fermi, many physicists alongside engineers are working to understand these neutrinos. We are building a massive experiment called the Deep Underground Neutrino Experiment (DUNE) to learn more. 

Check this out: at Fermilab, we create an intense beam of protons which are pointed at graphite (carbon) to produce pions, which quickly decay into muons and muon-type neutrinos.

Those muon-type neutrinos are aimed towards Sturgis, South Dakota, having to have been pointed downwards into the Earth at Fermilab because the Earth is a sphere.

At the depth of one mile, we are building a huge detector, sort of like a camera, to take “pictures” of the muon-type neutrinos interacting inside the detector, albeit in a rare process. I should mention that computer scientists are working with the DUNE physicists because the so-called camera images are mightily large, and we anticipate too many to count.

I alluded to this earlier, but neutrinos rarely interact with matter, and all those neutrinos going through your Sun-pointed finger, keep going, through the floor of your house, into the Earth, right on through the entire Earth, wow, and onwards going way way far away.

But occasionally, yes these neutrinos do interact. So what we have to do at Fermilab to encourage neutrino interactions is to make a whole bunch of them just to see a few of them tickle our deep underground detector.

So here’s the special part, told by colleagues on other particle physics experiments trying to do similarly to DUNE scientists, that is to figure out what a neutrino is. Together, we have learned that when a muon-type neutrino is created at Fermilab, and aimed through the 800 miles of rock between Illinois and South Dakota, some small fraction change into electron-type neutrinos.

To emphasize, we know how to identify the stuff that is “captured on film” in our detectors as the anticipated muon-type neutrinos make themselves known, and separately the unanticipated electron-type neutrinos. But where did the electron-type neutrinos come from, were they not first muon-type neutrinos?

It’s weird, it’s like the neutrino starts out as a cat, then as it travels to South Dakota, it somewhere became a bird. And when we also consider the tau-type neutrino in the process, the original cat became a dog.

Yeah, a cat can become a bird, and/or maybe a dog. If that could really happen you’d wonder if you were reading a Harry Potter book.

We call that ability to change flavor on-the-fly, neutrino oscillation, and unlike any other subatomic particle (almost) neutrinos are special, and we therefore want to know more.

In fact, as neutrinos are the most abundant particle in the universe, except for photons which is the name we use for the particle version of light. And studying the wierd characteristics of the neutrino is likely to get us an understanding on how the universe was first formed some ten billion years ago, and hopefully solving other problems such as, are protons for forever, or what Black Holes might be.

DUNE detectors will also be sensitive to the neutrinos produced when stars larger than our Sun explode – yes, stars are born, and stars die, and when they go, neutrinos are yet again a big part of the picture.

Will, I hope that this story inspires your curiosity.

Your friend, David 

More on DUNE: https://www.dunescience.org