K. Miuchi

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 room, a hunter waits for a barely audible rustle. Similarly, physicists have spent years listening for signals from dark matter particles — the invisible substance that holds galaxies together but doesn't emit light. The new detector makes this 'hearing' a hundred thousand times sharper. Inside the device is SF₆ gas (the same stuff that quenches sparks in electrical grids).

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.

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.