Why, after millions of years of steadily lighting the cold darkness, does a supergiant star suddenly explode in a blinding blaze of glory brighter than 100 billion stars? What exotic objects in deep space are firing out particles at by far the highest energies in the universe? And perhaps most mind-bending, why does the universe contain any matter at all? These mysteries have vexed astrophysicists and particle physicists for decades. The key to solving all three deep conundrums is itself one of the greatest enigmas of physics: the neutrino.
The universe is awash in these peculiar, nearly massless, subatomic particles. Created in tremendous numbers right after the Big Bang, and constantly churned out in stars and other places by radioactive decay and other reactions, trillions of these ghostly particles sail right through stars and planets, including our own.
Carrying no electrical charge, neutrinos are attracted neither to protons nor electrons, so they don’t interact with electromagnetic fields. They also don’t feel a powerful force that operates on tiny scales, known simply as the strong force, which binds protons and neutrons together in an atom’s nucleus.
Neutrinos are more aloof than supermodels, rarely interacting meaningfully with one another or with anything else in the universe. Paradoxically, it is their disengaged quality that earns them a crucial role both in the workings of the universe and in revealing some of its greatest secrets.
Neutrino physics is entering a golden age. As part of one experiment, neutrinos have recently opened a new window on high-energy sources in deep space, such as black holes spewing out particles in beams trillions of miles long.
