In a historic breakthrough for science, astronomers detected the most energetic “ghost” particle ever recorded in the history of physics at the bottom of the Mediterranean Sea. Using a massive network of sensors still under construction, the scientists were able to capture a neutrino with an impressive energy of 220 million billion electron-volts (220 PeV) — a value making it about 30,000 times more powerful than anything generated by the Large Hadron Collider (LHC) of the European Organization for Nuclear Research (CERN). This discovery, which opens a new chapter in neutrino astronomy, allows for a deep dive into the cosmic universe and the most extreme natural events.

To understand the magnitude of this discovery, it is essential first to comprehend the nature of neutrinos, the so-called “ghost” particles of the universe. Neutrinos are elementary particles with almost no mass and no electric charge. Their most notable feature is their ability to pass through matter without undergoing any change. In fact, neutrinos are so elusive that they can travel through planets, stars, and even entire galaxies without interacting with anything. This makes detecting these particles extremely difficult.

Neutrinos are produced in violent cosmic processes, such as supernova explosions, supermassive black holes, and cosmic rays traveling through space at nearly the speed of light. When these neutrinos reach Earth, they can only be detected under special conditions, due to their rare interaction with matter. One of their peculiar characteristics is that when they interact with water or ice, they emit a bluish light known as Cherenkov radiation, which can be registered by specialized sensors.

Because these particles are so volatile and hard to capture, they have always been seen as mysterious cosmic messengers, capable of revealing unique information about the universe’s most energetic events and what happens at the farthest reaches of the cosmos.

The record-breaking neutrino, named KM3-230213A, was captured on February 13, 2023, and its detection represented a significant milestone in particle physics. The amount of energy this particle carries is simply astonishing. To put it in perspective, the neutrino’s 220 PeV energy is equivalent to 30,000 times the energy produced by the LHC, the world’s largest particle accelerator, located in Switzerland. This value is so extraordinary that, as co-author of the study Brad K. Gibson explains, it is as if the energy released by the fission of a billion uranium atoms is contained in a single subatomic particle.

To illustrate how intense this energy is, Aart Heijboer, another co-author of the study, provides a simple yet revealing analogy: if the neutrino’s energy were converted to a more familiar scale, it would be equivalent to the energy of a ping-pong ball falling from a height of 1 meter. Although this value seems small in the context of the everyday world, the true magnitude of the discovery lies in the fact that a single particle is capable of containing such an extraordinary amount of energy.

Although it was detected on Earth, the origin of neutrino KM3-230213A remains a mystery. The KM3NeT research team, which made the detection, believes that it originated from cosmic events beyond the Milky Way. The big question is: what in the universe could generate a particle with such energy?

Among the possible sources are extreme and mysterious astrophysical events, such as:

• Supermassive black holes, whose intense gravitational fields can accelerate particles to extremely high energies.
• Gamma-ray bursts, cataclysmic phenomena that occur when massive stars collapse, releasing an enormous amount of energy.
• Supernova remnants, which are the explosions of massive stars that release large amounts of radiation and particles, including neutrinos.

Despite the research teams’ attempts to trace the trajectory of the neutrino, it is difficult to pinpoint exactly where it came from. The analysis of its direction indicated that it could have originated from a blazar, an active galaxy with a supermassive black hole at its core, capable of emitting jets of energetic particles toward us. In any case, it is still not possible to identify its origin with certainty, and further investigations will be needed to solve this cosmic enigma.

The detection of neutrino KM3-230213A was made possible thanks to the work of an international team that developed KM3NeT (Kilometer Cubic Neutrino Telescope), an innovative project aimed at detecting neutrinos from the depths of the ocean. Instead of building large particle accelerators on land, like the LHC, the idea was to use the underwater environment to capture the light signals generated when neutrinos interact with water.

KM3NeT consists of a series of underwater detectors spread across the Mediterranean Sea floor. The project is being built at two distinct locations:

• ARCA (Astroparticle Research with Cosmic Rays in the Abyss), located 3,450 meters deep near Sicily, Italy. This detector is specialized in capturing high-energy neutrinos.
• ORCA (Oscillation Research with Cosmic Rays in the Abyss), located 2,450 meters deep near Toulon, France, dedicated to the search for low-energy neutrinos.

Although the KM3NeT project is still under construction, impressive discoveries, such as the detection of high-energy neutrino KM3-230213A, have already been made. Interestingly, ARCA was operating at only 10% of its full capacity at the time of the detection. This indicates that when fully operational, KM3NeT will be able to capture even more energetic neutrinos and provide more information about the cosmic phenomena that generate these particles.

Detecting neutrinos requires cutting-edge technology, as these particles do not interact easily with matter. However, when a neutrino collides with a water or ice molecule, it can produce a blue glow that is captured by highly sensitive optical sensors. This phenomenon, known as Cherenkov radiation, was crucial in identifying neutrino KM3-230213A.

Another major challenge is that, while neutrinos are great cosmic messengers, their sources are hard to identify. Even with the detection of hundreds of neutrinos, as already done in observatories like IceCube at the South Pole, the correlation between the particles and their sources is still an open field. This is one of the aspects that makes neutrino astronomy such a fascinating field, because by understanding the origin of these neutrinos, scientists can learn more about the most extreme events in the universe.

The detection of a neutrino with this unprecedented energy is not only an impressive technical feat, but also an opening to new possibilities in the exploration of the universe. Astronomer Rosa Coniglione, co-author of the study, emphasized that neutrinos are “special cosmic messengers” because they carry unique information about the most enigmatic and energetic phenomena occurring in the cosmos. From these particles, we can begin to understand better events like cosmic rays, supernova explosions, and other large-scale phenomena.

The detection of neutrino KM3-230213A marks the beginning of a new phase in multi-messenger astronomy, which combines data from different sources — such as gamma rays, gravitational waves, and neutrinos — to provide a more complete view of cosmic phenomena. This new approach may not only expand our understanding of the universe, but also open doors to discoveries that, until now, seemed impossible.With the advancement of research, KM3NeT and other neutrino detection networks will be able to provide definitive answers about the origin of cosmic rays and the cosmic microwave background radiation, as well as uncover mysteries that could forever change our understanding of the cosmos.