Skip to Content Skip to Main Menu

Faculty of Arts & Science

Arts & Science News

Ray Jayawardhana on neutrinos — the most elusive particles in the known universe

Photo: Paola Scattolon

Photo: Paola Scattolon

Ray Jayawardhana is U of T’s resident space junkie, a Canada Research Chair in Observational Astrophysics whose research tends to focus on the truly “out there,” like exoplanets and brown dwarfs. But for his latest book, he turns his attention inward. Part detective story, part science journal, Neutrino Hunters: The Thrilling Chase for a Ghostly Particle to Unlock the Secrets of the Universe is about the search for the most elusive particle in the known universe, trillions of which pass through our bodies every second.

Jayawardhana’s pursuit takes him from an Ontario nickel mine to the Swiss Alps, from a nuclear waste site in New Mexico to the South China Sea, and from the University of Toronto to Antarctica’s IceCube, the world’s largest neutrino detector. In advance of a public Q&A with Jayawardhana at the Toronto Reference Library on February 13, A&S News caught up with him for a few questions of our own about neutrinos and what they mean for the study of everything from supernovas to antimatter to the origin of the universe.

A&S: Neutrinos sound like something from Star Trek, and they’ve popped up in pop culture many times, such as in The Big Bang Theory. Can you explain what they are?

RJ: Neutrinos are a type of elementary particle — tiny specks of matter, with rather quirky characteristics, you might say. Since they hardly interact with their surroundings, these ghostly particles are extremely difficult to pin down. So scientists have had to build huge detectors underground and deep under the ice to trap just a handful of the many trillions that pass by every second.

A&S: In your book you describe neutrinos as “pathologically shy.” How do we know they even exist?

RJ: Their severe reluctance to mingle makes neutrino hunting a tricky business. But every so often, a neutrino does collide with something, such as an atomic nucleus, essentially by accident. Even then, you can’t see neutrinos directly, but you can get a whiff of their presence from the clues they leave behind. On the rare occasions that neutrinos do interact with matter, they produce charged particles, such as muons, that physicists can detect with their instruments.

A&S: Neutrinos may help us answer some big questions about the Big Bang and why stars explode. Can you explain how they are able to do this?

RJ: Since neutrinos are produced in nuclear reactions associated with a wide variety of cosmic phenomena, they can reveal a lot about extreme events in the universe, like supernova explosions. So far, scientists have detected only a handful of neutrinos coming from beyond our solar system. The first batch of cosmic neutrinos was captured in 1987, from a star that exploded in a satellite galaxy of the Milky Way. Last November, scientists using the IceCube observatory in Antarctica reported the discovery of energetic neutrinos, likely coming from jets launched by supermassive black holes at the hearts of galaxies or exploding stars.

A&S: It seems strange that in order to understand the vastness of the universe we must study the smallest of particles. Thoughts?

RJ: Indeed, there are intimate connections between the biggest and the smallest scales of matter, between cosmology and particle physics. The characteristics of the tiniest particles influence the largest cosmic structures, and the evolution of the universe itself.