A recent study using the XENONnT dark matter detector has made a significant discovery: it has observed low-energy solar neutrinos interacting with electrons for the first time. This observation reached a statistical significance of 5 sigma, which is the standard threshold for declaring a discovery in particle physics. These neutrinos are produced by the proton-proton fusion reactions that power the Sun and make up the majority of its neutrino emissions. XENONnT is the latest version of a detector developed over decades and located 1,400 meters beneath the Gran Sasso mountain in Italy. It contains 5.9 tons of ultra-pure liquid xenon, which allows it to detect and measure the passage of these solar neutrinos. Neutrinos are subatomic particles with no electric charge and very little mass, which allows them to pass through matter almost undisturbed. They are far more numerous than the photons of the cosmic microwave background and even more so than the particles that make up ordinary matter. Detecting these neutrinos confirms a key theory about the Sun’s energy production that dates back to the 1930s. This theory, developed alongside the rise of quantum theory and nuclear physics, explains how the Sun produces energy through nuclear fusion. The proton-proton chain, first described by physicist Hans Bethe, is the main process by which the Sun converts hydrogen into helium, releasing energy in the process. The XENONnT detector’s large volume of ultra-pure liquid xenon and its exceptionally low levels of radioactive contamination, especially radon, have made it one of the most sensitive neutrino detectors in the world. This sensitivity allows it to observe rare interactions of low-energy particles, which are otherwise extremely difficult to detect. Neutrino research has important implications in astrophysics and cosmology, including understanding the energy sources that power stars like the Sun. Because neutrinos are so penetrating, they can travel through 300 Earths lined up side by side before being stopped, making them a unique tool for studying the core of the Sun and testing theories about how stars function. This discovery not only confirms long-standing scientific models but also opens new avenues for exploring the universe’s most elusive particles.