Neutrinos: Catch the ghost particles, crack the cosmic code

Every second, trillions of neutrinos pass through your body. They slip through flesh, rock and even the entire Earth, leaving virtually no trace. You cannot feel them, and detecting them is extraordinarily difficult.

Yet, these elusive particles could help scientists answer some of the biggest questions about the universe: What happens inside exploding stars? What powers the most extreme objects in space? And why is the universe made predominantly of matter when antimatter should also have been created?

The 2026 Nobel Prize in Physics, awarded to physicist Francis Halzen for his decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin, has brought these ghost-like particles into the spotlight. By tracking particles rather than relying on light alone, scientists have opened a new window into the universe, one that could reveal things even powerful telescopes cannot easily see.

What makes neutrinos special? Neutrinos are elementary particles produced in the Sun, nuclear reactions, supernova explosions and other energetic astrophysical processes. They have no electric charge and interact primarily through the weak nuclear force.

This means they can travel enormous distances through matter and magnetic fields without being significantly absorbed or deflected. Light can be blocked, scattered or absorbed on its journey through space. Neutrinos, by contrast, can escape dense cosmic environments and reach Earth carrying information about the processes that produced them.

“Neutrinos are extraordinarily abundant but interact so weakly with matter that they can travel through stars and planets largely undisturbed. They offer unique insights into stellar interiors, supernova explosions and extreme astrophysical environments,” said Prof Basudeb Dasgupta of the Department of Theoretical Physics at the Tata Institute of Fundamental Research (TIFR).

How do you catch a particle that passes through the Earth? The very property that makes neutrinos valuable also makes them difficult to detect. Because they rarely interact with matter, scientists cannot simply observe them passing through a detector.

Instead, they wait for the occasional collision that produces detectable signals. At the IceCube Neutrino Observatory, thousands of light sensors are embedded deep within Antarctic ice, covering an instrumented volume of about a cubic kilometre. When a neutrino collides with an atom in the ice, it can produce charged particles that emit faint flashes of light.

By studying these flashes, researchers can estimate the neutrino’s direction and energy. “It is very hard because neutrinos interact very weakly. You need big detectors with lots of photomultiplier tubes, and you have to go to extreme environments such as the South Pole,” said Prof Shantanu Desai, professor in the Department of Physics at IIT Hyderabad and an adjunct faculty member in its AI department.

What has IceCube revealed? Detecting neutrinos is only the beginning. Scientists also want to know where they come from and what produced them.

In 2017, IceCube detected a high-energy neutrino associated with a flaring active galactic nucleus, a region surrounding a supermassive black hole. The observation helped establish a link between such cosmic environments and high-energy neutrinos, offering researchers a way to investigate some of the universe’s most energetic processes.

But the mystery is far from solved. Scientists still do not know the origins of most high-energy astrophysical neutrinos detected by IceCube. Identifying their sources and understanding how they acquire such enormous energies remain major research challenges.

Can neutrinos explain why matter won? Look around, and almost everything you see is made of matter. Yet, according to our understanding of the early universe, matter and antimatter were both produced.

Antimatter particles have properties related to those of their matter counterparts, and when the two meet, they can annihilate each other. So why did matter come to dominate the universe? Scientists have yet to establish the full explanation.

One possible clue lies in charge-parity (CP) symmetry, which concerns how physical processes compare with those involving antimatter. Researchers are investigating whether neutrinos violate this symmetry through a process called neutrino oscillation, in which they change from one flavour to another as they travel.

“Theoretically, there is an intimate connection between the question of matter-antimatter asymmetry and the properties of neutrinos. Experimentally, however, establishing this connection is hard,” said Dasgupta. Prof Rukmani Mohanta, senior professor in the Department of Physics at the University of Hyderabad, said, “Neutrinos could help scientists investigate the origins of this matter dominance.

The universe is composed predominantly of matter, but we do not yet fully understand what happened to antimatter. One possibility being investigated is whether additional sources of CP violation could be associated with neutrinos.”