• KM3NeT detected a 220 PeV neutrino, the highest-energy neutrino ever observed, far exceeding energies produced by the Large Hadron Collider.
• The origin of the neutrino is unknown, with possibilities including a blazar or being a cosmogenic neutrino, created by high-energy cosmic rays colliding with cosmic microwave background radiation.
• This discovery opens a new chapter in neutrino astronomy, offering a unique window into the universe's most violent phenomena and potentially uncovering physics beyond the Standard Model.

The KM3NeT detector, located deep in the Mediterranean Sea, detected a neutrino with an estimated energy of 220 peta-electronvolts (PeV) on February 13, 2023. This is the most energetic neutrino ever observed, surpassing previous detections by orders of magnitude. The neutrino's origin is currently unknown, prompting further investigation into potential sources such as blazars or the more elusive cosmogenic neutrinos. This detection underscores the potential of neutrino astronomy to provide unique insights into high-energy astrophysical processes.

• What: Detection of a 220 PeV neutrino by the KM3NeT detector in the Mediterranean Sea.
• Who: Paschal Coyle (physicist at the Centre for Particle Physics of Marseille), Rosa Coniglione (deputy spokesperson for KM3NeT), Naoko Kurahashi Neilson (neutrino astronomer at Drexel University), Shirley Li (physicist at the University of California, Irvine), Yuri Kovalev (Max Planck Institute for Radio Astronomy), Ryan Nichol (University College London), and the KM3NeT Collaboration.
• When: The neutrino was detected on February 13, 2023. KM3NeT is expected to be completed around 2029.
• Where: The neutrino was detected by the KM3NeT detector located three kilometers beneath the Mediterranean Sea.

The detection of this ultra-high-energy neutrino is significant because it opens a new window into the universe's most extreme environments. Neutrinos, unlike charged particles, travel in straight lines unaffected by magnetic fields, making them ideal messengers from distant sources. The fact that the origin of the neutrino is unknown presents a compelling mystery and motivates further investigation into potential sources such as blazars or cosmogenic neutrinos. If it's cosmogenic, it would be the first direct evidence that these highest-energy neutrinos truly exist. Future research and the completion of KM3NeT, along with other neutrino observatories, promise to reveal even more about these enigmatic particles and their role in the cosmos.

When I first tried looking at this event, my program crashed.

They are special cosmic messengers that reveal the secrets of the most energetic phenomena in the universe.

This first ever detection of a neutrino of hundreds of PeV opens a new chapter in neutrino astronomy.

It was really surprising. How does a smaller detector that’s been turned on for a shorter period of time see the rarest of them all, the highest-energy neutrino?

They did not identify any convincing source.

It is a very exciting possibility.

It’s challenging to say this event is from a cosmogenic flux.

By adding observations from other telescopes, we seek to connect the acceleration of cosmic rays, the production of neutrinos, and the role of supermassive black holes in shaping these energetic phenomena.

There are huge implications for science and astronomy.

If neutrinos are their own antiparticle, that might explain where all the antimatter in the early universe went.

This is a whole new arena in which to look for deviations.

This event shows their detector works beautifully. There’s so much more you can do with two detectors versus one. We are moving towards ultra-high-energy neutrino astronomy.

The detection of the 220 PeV neutrino by KM3NeT marks a groundbreaking moment in neutrino astronomy, confirming the existence of neutrinos at such extreme energies and opening a new observational window into the universe's most energetic phenomena. Its potential origins may lie in supermassive black holes, supernova explosions, or even more exotic sources like dark matter decay, although the precise source remains elusive, necessitating further investigation through multi-messenger astronomy. As KM3NeT and other neutrino observatories like IceCube, ANTARES, Baikal-GVD, and the future IceCube-Gen2 continue to expand and refine their detection capabilities, the prospects for unraveling the mysteries of cosmic ray acceleration, identifying specific astrophysical sources, and probing fundamental neutrino properties are greatly enhanced, potentially revolutionizing our understanding of the cosmos and particle physics. Future research should focus on detecting more high-energy neutrino events, improving neutrino beam identification techniques, and correlating neutrino observations with other astronomical signals to pinpoint the sources and fully understand the implications of these energetic messengers.