Astroparticle Physics

Francis Halzen explains how the IceCube telescope uses detectors buried deep in Antarctic ice to observe high-energy neutrinos from the cosmos. The lecture describes construction of the observatory, the measurement of particle energies and directions, and the distinction between atmospheric backgrounds and neutrinos arriving from distant astrophysical sources. It connects the discovery of cosmic neutrinos with the search for the powerful accelerators that produce cosmic rays. Examples include the association with a flaring blazar and evidence identifying the active galaxy NGC 1068 as a neutrino source. Halzen discusses the role of rotating supermassive black holes, coordination with other observatories, and prospects for extending the detector.

Hamish Johnston is joined by Oxford neutrino physicist Kirsty Duffy and Physics World's Matin Durrani to discuss the 2026 physics Nobel Prize awarded to Francis Halzen. They examine the IceCube observatory's contribution to detecting high-energy neutrinos from astrophysical sources and the broader history of Nobel-recognized neutrino research. The episode considers why these elusive particles have repeatedly transformed physics and how studying them opens a window onto the universe.

Ali Kheirandish reviews how high-energy neutrinos are reshaping multimessenger astronomy and searches for new particle physics. IceCube established the astrophysical neutrino signal in 2013; a decade of observations has since revealed directional structure, with emission identified from nearby active galaxies and a smaller contribution from the Milky Way. The seminar examines these measurements, the emerging account of where cosmic neutrinos originate, and opportunities to test physics beyond the Standard Model through the neutrino sector.