G. Bruni

Dark matter is the invisible glue that keeps galaxies from falling apart. Back in the 1930s, Fritz Zwicky suspected its existence, and in the 1970s Vera Rubin proved that without it, stars would fly apart.

In a dark mine under the Italian Alps, a tank holds three tons of liquid xenon. When a particle hits it, it knocks faint flashes of light and electron clouds out of the atoms. Following these tracks, physicists hope to see an ultra-rare decay: a xenon-136 nucleus turning into barium-136, emitting two electrons and no neutrinos.

Radio telescopes have caught a signal that repeats like a beacon in the fog. It's a fast radio burst — a brief flash of radio waves from a distant galaxy. Nearby, astronomers search for a persistent source — a faint glow that lingers after the burst, like embers after fireworks.

Deep beneath the Apennine Mountains, in a tank holding three tons of liquid xenon, something gives a barely perceptible shudder every few days. It's a solar neutrino, a ghostly particle born in the Sun's thermonuclear furnace, that has traveled 150 million kilometers through empty space and solid rock to finally collide with a xenon nucleus.

Nearly 12 billion years ago, when the Universe was experiencing the turbulent 'cosmic noon'—the era of record-breaking star formation — at the heart of one galaxy, the quasar WISSH13 was flaring up.