A ghostlike particle from deep space sent astronomers chasing one of the Universe’s hardest mysteries. The trail led somewhere unexpected. Instead of a ravenous black hole, the signal appears linked to a distant galaxy packed with fast, furious star formation. The particle was a high-energy neutrino, detected on Sept. 22, 2021, by the IceCube Neutrino Observatory at the South Pole. Known as IC 210922A, the event carried an energy of about 750 teraelectronvolts. It ranked among IceCube’s most notable alerts that year. Neutrinos are notoriously difficult to trace. They rarely interact with matter, which makes them useful cosmic messengers but frustrating ones. Although a few galaxies have already been tied to neutrino production, those known sources still do not explain the full background of high-energy neutrinos arriving at Earth. When an international team followed up on IC 210922A with the Atacama Large Millimeter/submillimeter Array, or ALMA, and other observatories, they found an unusually bright galaxy about 11 billion light-years away. Consequently, it became the prime suspect. This image shows the gravitationally lensed galaxy nicknamed “Shadow …