Reacción a "Nobel Prize in Physics Awarded to Francis Halzen for the discovery of high-energy neutrinos of astrophysical origin and for his “decisive contributions” to the IceCube Observatory"

It is a well-deserved award. Professor Halzen, whom we met just two weeks ago, not only proposed the idea of using Antarctic ice as a natural medium for detecting neutrinos, but also pursued this idea with extraordinary determination, even when it was unclear whether a volume of one cubic kilometer would be sufficient to detect the weak neutrino fluxes at those energies.

The “window” into the universe of very high-energy astrophysical neutrinos has gradually opened: first, with the detection of neutrinos coming from all directions, without it being possible to identify their sources; then, with the identification of a transient signal from an active galaxy; later, with the detection of a continuous signal from a nearby galaxy; and, finally, with the identification of neutrinos originating from our own galaxy.

It is, therefore, a tribute to Professor Halzen’s leadership and his determination to overcome a countless series of difficulties and bring to fruition the idea he himself had conceived. It is also a recognition of the IceCube collaboration and its extraordinary scientific, technical, and logistical achievements, and, finally, an endorsement of an entire field: very-high-energy neutrino astrophysics. 

More specifically, the Nobel Prize was awarded for the discovery of very high-energy astrophysical neutrinos. The idea that very high-energy neutrinos produced in extremely energetic phenomena in the universe could be observed using large natural bodies of water dates back to 1960. However, the proposal to use Antarctic ice as a detection medium was formulated by Francis Halzen and a collaborator in 1988. 

Professor Halzen did not merely propose the idea; rather, with extraordinary leadership and great perseverance, he worked for more than two decades to make it a reality. In 2011, after seven years of construction, IceCube (“the ice cube”) began operating—a detector that occupies more than one cubic kilometer of ice at a depth of over 1,500 meters beneath the surface of Antarctica. 

Two years later, in 2013, IceCube made its first detection of very high-energy neutrinos from astrophysical sources located beyond our galaxy, although it was not yet possible to identify their origin. In 2018, a specific source was identified for the first time: a blazar, an active galaxy whose powerful jet of particles points roughly in the direction of Earth. In 2022, IceCube obtained evidence of a continuous neutrino emission from the spiral galaxy M77 (NGC 1068). And a year later, in 2023, it was confirmed that our own galaxy, the Milky Way, is also a source of very high-energy neutrinos.