University of Wisconsin-Madison physicist Francis Halzen has been awarded the 2026 Nobel Prize in Physics for his contributions to understanding astrophysical neutrinos. Halzen led the development of the IceCube Neutrino Observatory beneath the Antarctic ice, which has helped trace high-energy neutrinos back to cosmic sources such as supermassive black holes and opened a new era of "multi-messenger" astronomy. Longtime Slashdot reader schwit1 shares a report from UW-Madison: Embedded in a cubic kilometer of Antarctic ice, IceCube uses thousands of light sensors to survey the universe for neutrinos, nearly massless particles that rarely interact with other matter. Neutrinos provide information about the workings of black holes, galaxies and other objects in the cosmos. "IceCube is like no other telescope in the world," says UW-Madison interim Chancellor Eric M. Wilcots. "And there is no other scientist quite like Francis Halzen, whose idea to create a neutrino detector under almost a mile of ice has led to a remarkable multinational and multi-institutional scientific collaboration and a fundamental shift in how we think about the universe." Unlike the neutral neutrino, cosmic rays are charged particles whose paths cannot be traced directly back to their sources. But the powerful cosmic accelerators that produce them, like supermassive black holes, will also produce neutrinos. These so-called "ghost particles" travel nearly undisturbed from their accelerators, giving scientists an almost direct pointer to their source. Along with observations by other telescopes, the neutrino first detected by IceCube provided the first-ever evidence of a source of high-energy cosmic rays, whose origins have been notoriously difficult to pinpoint since their discovery over 100 years ago by 1936 physics Nobel laureate Victor Hess.

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