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Neutrinos change their flavor just as chameleons can change color. The observer needs to make sure their instruments are prepared to detect these changing beasts.
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We don’t know much about neutrinos, but what we do know points to renegade particles that, despite their prevalence, are hard to pin down. Here are, in a nutshell, nine neutrino nuggets that scientists have figured out so far.
1.Neutrinos are super abundant. The shining sun sends 65 billion neutrinos per second per square centimeter to Earth. Neutrinos are the second most abundant particle in the universe. If we were to take a snapshot, we’d see that every cubic centimeter has approximately 1,000 photons and 300 neutrinos.
2.Neutrinos are almost massless. No one yet knows the mass of neutrinos, but it is at least a million times less massive than the lightest particle we know, the electron. We do know that each is so lightweight and so abundant that the total mass of all neutrinos in the universe is estimated to be equal to the total mass of all of the visible stars.
3.Neutrinos are perfect probes for the weak force. All other fundamental particles interact through the strong, electromagnetic or weak force or through some combination of the three. Neutrinos are the only particles that interact solely though the weak force. This makes neutrinos important for nailing down the details of the weak force.
4.Neutrinos are really hard to detect. On average, only one neutrino from the sun will interact with a person’s body during his or her lifetime. Since neutrino interactions are so rare, neutrino detectors must be huge. Super Kamiokande in Japan is as tall as Wilson Hall and holds 50,000 tons of ultrapure water. IceCube is buried between 1.5 and 2.5 kilometers under pure and clear ice in Antarctica, instrumenting a full cubic kilometer of ice.
5.Neutrinos are like chameleons. There are three flavors of neutrinos: electron, muon and tau. As a neutrino travels along, it may switch back and forth between the flavors. These flavor “oscillations” confounded physicists for decades.
6.Neutrinos of electron flavor linger around electrons. When neutrinos travel through matter, they see dense clouds of electrons. Electron neutrinos will have trouble traversing these dense clouds, effectively slowing down while muon and tau flavors travel through unimpeded. The NOvA experiment is using this phenomenon to deduce more information about the neutrino masses.
7.Neutrinos let us see inside the sun. The light that reaches Earth takes 10,000 to 100,000 years to escape the thick plasma of the sun’s core. When light reaches the solar surface, it freely streams through open space to our planet in only 8 minutes. Neutrinos provide us a penetrating view into the core, where nuclear fusion powers the sun. They take only 3.2 seconds to escape to the solar surface and 8 minutes to reach Earth.
8.Neutrinos may have altered the course of the universe. Why is everything in the universe made predominantly of matter and not antimatter? Cosmologists think that at the start of the universe there were equal parts of matter and antimatter. Neutrino interactions may have tipped this delicate balance, enabling the formation of galaxies, stars and planets like our own Earth.
9.Neutrinos dissipate more than 99 percent of a supernova’s energy. Certain types of stellar explosions lose nearly all of their energy through neutrinos. These “core collapse” supernovae end as either a black hole or a neutron star. Neutrinos are used to understand how supernovae explode and tell us more about other astronomical objects like active galactic nuclei.
—Tia Miceli