Particles flying from space to Earth contain clues to the origin of the universe and various secrets. In particular, neutrinos are considered important clues to unraveling the mysteries of the universe, being emitted from Taeyang, supernovae, black holes, and neutron stars. Recently, an international research team successfully captured cosmic neutrinos with the highest energy ever.
Researchers from the cubic kilometer neutrino telescope (KM3NeT) project noted that they captured neutrinos with about 30 times the energy of previously detected neutrinos, suggesting they likely came from deep space beyond our galaxy. The research findings were published in the international journal "Nature" on the 13th.
Neutrinos are one of the fundamental particles that make up matter, being more than a million times lighter than electrons. They are referred to as the "ghost particle" of the universe because they pass through all kinds of matter and interact almost not at all with surrounding materials, including protons and neutrons. Approximately 100 trillion neutrinos pass through the human body every second, but detecting them is extremely difficult.
To capture neutrinos, scientists place thousands of extremely sensitive sensors deep in the mountains or in transparent ice and water to detect neutrinos. Other particles cannot easily pass through ice or water, allowing for background correction. When high-energy neutrinos collide with matter, charged particles are created, emitting blue light, which can confirm the presence of neutrinos.
This discovery was made through KM3NeT. The telescope consists of two detectors installed on the seabed of the Mediterranean near Sicily, Italy, and Provence, France. The researchers have been collecting data even before the telescope was fully constructed and recently confirmed that they detected high-energy signals from the fundamental particle "muon" on Feb. 13, 2023. Muons are subatomic particles generated when neutrinos collide with rocks or seawater near the detector.
Analysis revealed that the muon had a nearly horizontal trajectory concerning the Earth's surface and had enough energy to be detected even at deep-sea detectors. Based on this, the researchers estimated that muons came from neutrinos with an energy of about 2.2 trillion electron volts (eV). This amount is equivalent to dropping a ping pong ball from a height of 1 meter and is tens of thousands of times more than the energy obtainable from the Large Hadron Collider (CERN), the world's leading particle accelerator.
The research team examined various possibilities to find the origin of the neutrinos. First, they selected 12 candidate blazars, which are central black holes of galaxies that align with the direction from which the neutrinos came. However, they have not yet determined an exact origin. Another possibility is that these could be "cosmic-generated neutrinos" created when high-energy particles comprising cosmic rays collide with photons from cosmic background radiation. The researchers noted, "We plan to investigate the origin of the particles by identifying the direction of the neutrinos more accurately."
Yoon-tae, a professor of physics at Sungkyunkwan University, said, "While light coming from space can be absorbed, reflected, or refracted, neutrinos can be seen as a telescope that allows us to see the universe transparently since they do not distort. We do not yet fully understand the mechanisms in the universe that produce high-energy neutrinos, but this research provides an important clue to understanding that."
References
Nature (2025), DOI: https://doi.org/10.1038/s41586-024-08543-1