Hidden deep beneath Mount Ikeno in Japan lies a monumental experiment—Super-Kamiokande. This colossal neutrino detector is a physics marvel that occupies the space equivalent to a 15-story building. Its mission? To catch the most elusive particles in the universe.
The Unseen World of Neutrinos
Neutrinos are subatomic particles that travel through space at nearly the speed of light, passing effortlessly through solid matter without interacting.
In fact, they are so elusive that renowned astrophysicist Neil deGrasse Tyson once described them as “the most elusive prey in the cosmos.”
The challenge with neutrinos is that they are incredibly difficult to detect due to their ability to pass through objects without leaving a trace.
Tyson emphasizes, “Matter poses no obstacle to a neutrino. A neutrino could pass through a hundred light-years of steel without even slowing down.”
Despite their invisibility, neutrinos hold the key to understanding some of the universe’s most violent and fascinating events, including supernovae—the explosive deaths of massive stars.
“If there’s a supernova, a star that collapses into itself and turns into a black hole… if that happens in our galaxy, something like Super-K is one of the very few objects that can see the neutrinos from it,” Dr. Yoshi Uchida of Imperial College London explains.
Before a star collapses, it releases neutrinos in vast quantities, and Super-Kamiokande can detect these particles, providing an early warning of a supernova event.
The neutrino is the most abundant particle in the universe – but also the most elusive. Finding neutrinos requires large, complicated experimental set-ups like the Super-Kamiokande detector, which is located beneath Mount Ikeno in Japan and the result of an international… pic.twitter.com/R7AVFVnVuX
— The Nobel Prize (@NobelPrize) March 9, 2025
A Deep Dive into Super-Kamiokande’s Lab
Super-Kamiokande is far more than just a massive chamber. Situated 1,000 meters underground, it is designed to be an ideal environment for detecting the elusive neutrinos.
The detector is filled with 50,000 tonnes of ultra-pure water, which plays a crucial role in the detection process.
Neutrinos, traveling faster than light in water, produce a shockwave of light as they pass through, a phenomenon known as Cherenkov radiation.
This is where the true magic of Super-Kamiokande comes into play. The chamber is lined with 11,000 highly sensitive light detectors called Photo Multiplier Tubes (PMTs) that are capable of picking up these faint bursts of light.
Dr. Uchida draws an interesting analogy: “If an aeroplane is going very fast, faster than the speed of sound, then it’ll produce sound — a big shockwave — in a way a slower object doesn’t. In the same way, a particle passing through water, if it’s going faster than the speed of light in water, can also produce a shockwave of light.”
The Role of Ultra-Pure Water
The water in the Super-Kamiokande detector is nothing short of extraordinary.
Not only is it exceptionally clear, but it also possesses an almost dangerous level of purity. Dr. Uchida warns, “Pure water is very, very nasty stuff. It has the features of an acid and an alkaline.”
This ultra-pure water has the ability to dissolve metals, and even the tiniest impurities can interfere with the delicate measurements the detector is designed to make.
In fact, the ultra-pure water has proven to be so aggressive that it is known to leach nutrients from organic materials.
Dr. Matthew Malek, a researcher at the University of Sheffield, recalls an eerie experience during a maintenance session: “I got up at 3 o’clock in the morning with the itchiest scalp I have ever had in my entire life. It was so itchy I just couldn’t sleep.”
He later realized that the ultra-pure water had extracted nutrients from his hair. “It had leeched my hair’s nutrients out through the tips,” he said.
A System to Detect the Death of Stars
Super-Kamiokande doesn’t only detect neutrinos from supernovae. For instance, it plays a pivotal role in the T2K experiment, where neutrinos are fired across Japan to study how they oscillate as they pass through matter.
As Dr. Morgan Wascko of Imperial College London notes, “Our big bang models predict that matter and anti-matter should have been created in equal parts, but now [most of] the anti-matter has disappeared through one way or another.”
Super-Kamiokande has been instrumental in providing the “strongest evidence yet” that matter and anti-matter behave differently, helping scientists better understand why matter exists in the universe.
