axion dark matter search

Picture a radio receiver with a single tuning knob that moves all of its internal coils at once, like one living organism. That is exactly how a new instrument for the search for the axion works, a particle that may fill galaxies with invisible mass. Inside a copper cylinder the height of a coffee can sit rods of aluminum oxide.

In the basement of the laboratory, an 8 tesla magnet hums. Inside it, like a bell in a bell tower, hangs a hollow copper cylinder tuned to a single note. If an axion, a dark matter particle, flies by, the cylinder responds with a faint ring. The trouble is that ordinary copper muffles this ring: at high frequencies, current flows only through a thin skin of the metal, and losses grow.

The night forest is full of fireflies, but before, we only saw those that happened to be in the beam of a flashlight. That was the case with ultraluminous X-ray sources: points in other galaxies that shine in X-rays more brightly than a stellar-mass black hole can steadily emit. Telescopes looked at galaxies chosen for other purposes, missing most of the fireflies.

264 kilometres per second — that's how fast the Solar System hurtles through the cloud of dark matter. Its existence was given away by galaxies: they spun too fast to be held by visible mass, and Vera Rubin was first to suspect a hidden scaffolding.

A lighthouse at sea doesn't just rotate: its lamp itself dims and brightens on its own. Magnetic white dwarfs, the ultra-dense remnants of stars like our Sun, behave in much the same way. Their powerful magnetic fields can convert light into axions — hypothetical particles that could explain the Universe's hidden mass.

Half a century ago, Fritz Zwicky noticed that the visible matter in galaxy clusters was catastrophically insufficient to explain gravity.

In the pitch darkness of a vacuum chamber, a tiny magnet floats. It touches no walls and loses almost no energy — an ideal sentinel, ready to catch the faintest nudge. Such a sentinel is exactly what you need for axion hunting. These particles are prime suspects in the case of the Universe's hidden mass, which we call dark matter.

The universe is permeated by invisible mass, dark matter, whose existence was first proposed by Fritz Zwicky in the 1930s, based on his observations of galaxies moving in clusters.

Think of a baby mobile: figurines dangling on threads, twitching at even a whisper of breeze. In the same way, planets on very wide orbits barely cling to their star's gravity, and they feel the faintest gravitational drafts. Astronomers have proposed turning such planets into detectors of dark matter.

An ocean permeates all of space, yet remains invisible to us. This ocean is dark matter, and the waves on its surface are particles called axions. They are so light and elusive that they pass through Earth without noticing it. But if these waves crash against a shore made of a special material, they might leave a trace — a tiny electric current.

Imagine a translator working in a noisy hall. The hum of voices, the clatter of dishes, fragments of other people’s conversations: it seems they should constantly make mistakes. But by the end of the day, their notes match perfectly with what they would have written in the quiet of an office. This is roughly how the quantum rule known as the axial anomaly behaves.

The story began with a puzzle: in the 1930s, Fritz Zwicky noticed that clusters of galaxies behave as if an enormous invisible mass is hidden within them. Half a century later, Vera Rubin confirmed that stars on the outskirts of galaxies rotate too fast to be held by visible matter alone.

Dark matter is an invisible substance that reveals itself only through gravitational effects: it bends the light of distant galaxies, much like an unseen window that alters the path of light rays.

The story began almost a century ago, when Edwin Hubble showed that galaxies are receding, and Fritz Zwicky and Vera Rubin later realized: to explain their motions, invisible mass is needed — dark matter.

A lighthouse spins in dense fog. Its beam cuts through the gloom, but the fog itself remains invisible. That's roughly how astronomers search for dark matter: it doesn't emit light, yet it can affect the signals that reach us.

Light passing by a black hole falls into a gravitational trap: its trajectory curves and the particle bounces along a nearly closed orbit, like a pinball.

The universe is full of invisible substance that governs the movement of galaxies. In the 1970s, astronomer Vera Rubin showed: without dark matter, stars on the outskirts would have long since flown apart. But what it's made of remains unknown.

Dark matter is invisible, but its gravity governs the motion of galaxies. What it's made of is a mystery. One idea: it consists of ultra-light particles akin to axions.

In a noisy city, you try to hear a cricket. It's quiet, and cars are humming all around. To catch its chirp, you set up a sensitive microphone and hit the noise-cancellation button. That's roughly how physicists hunt for axions — hypothetical particles that could be the very dark matter holding galaxies together.

A tiny ring of superconductor, cooled to near absolute zero, could feel the touch of a particle billions of times lighter than an electron. We're talking about the axion — a hypothetical particle that might make up the dark matter filling the universe.

At the Large Hadron Collider, protons collide at nearly the speed of light. Sometimes they don't smash apart but exchange photons — particles of light. These photons can produce a pair: one particle the detector sees, and another that flies off unnoticed.

The kaon is a long-lived particle by microcosm standards: it lives for billionths of a second before breaking apart into lighter particles. In the KOTO experiment in Japan, physicists catch the rarest variants of such decays. One of them is when a kaon transforms into two neutral pions plus another particle X, which immediately decays into two photons (particles of light).

Black holes aren't silent abysses, but nature's tuning forks. Their rapid spin, predicted by Roger Penrose, makes spacetime itself sing, producing a stream of the lightest particles — axions. These accumulate around the hole, like sound in a concert hall, and begin to oscillate in unison.

Deep in a Canadian mine, there's a barrel holding 3269 kilograms of liquid argon — a clear fluid that looks like very cold water. This barrel is the DEAP-3600 detector, and its job is to catch dark matter particles, which are thought to permeate the universe but barely interact with ordinary matter.

Deep in the Swiss Alps, there is a vertical shaft that plunges 800 meters down, like two skyscrapers stacked on top of each other. A railway tunnel runs nearby, and trains thunder through it every day. But inside the shaft, it is as quiet as a library at night.

The universe is held together by an invisible scaffolding of dark matter. Part of it could be dark photons, ghostly copies of light that pass right through matter. The Dandelion experiment turned a spherical mirror into a super-sensitive ear: it gathers dark photons and translates them into the language of radio waves.

Deep in the Italian Apennines, under a thick layer of rock, sits a crystal that catches every decay of radioactive americium. Americium emits gamma rays with an energy of 59.5 kiloelectronvolts, like a very sharp bell that always sounds the same.

In a dark matter detector, the gas acts like photographic film: a passing particle leaves a track of free electrons and ions. But how bright that track is depends on exactly how the particle loses energy in the gas. For light ions like fluorine, the data have been imprecise.

Light from the star HD 163296 passes through the surrounding gas-and-dust disk like a flashlight beam through murky water. The disk's particles scatter the light, giving it a special property — polarization: the waves begin to oscillate in a single plane, like a rope shaken strictly up and down.

In the dark chamber of the detector, argon waits. When an invisible particle (say, a dark matter candidate) flies through, it gives the argon nucleus a gentle shove. The nucleus is knocked out of place, and charges are born around it. Exactly how many charges is no trivial question: physicists use that number to tell what kind of visitor dropped by.

Hidden in the heart of the Alps is the Large Hadron Collider. From time to time its detectors register sudden bursts — scientists call them UFOs (Unidentified Falling Objects). According to one theory, these are not equipment malfunctions at all, but traces of dark matter.

A bullet that doesn't just pierce one target but leaves marks in several layers of armor. That's roughly how superheavy dark matter behaves, and it's what the DarkSide-50 detector was built to catch for the first time. The usual suspects for dark matter (weakly interacting massive particles, or WIMPs) pass through matter almost unnoticed, occasionally bumping into a nucleus.

A metal resonator, chilled to near absolute zero, listens to the radio noise of the universe. Amid the chaos of thermal fluctuations and electronics, a faint peak might emerge — the trace of an axion, a particle that could make up dark matter.

A pot on the stove rings when the water boils. An empty copper cup can also "ring"—at radio frequencies — if a dark matter particle is born inside it. These particles are called axions, and according to one hypothesis, they fill the entire galaxy as an invisible cloud.

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.

The LCLS-II X-ray laser in California fires short, powerful flashes, like a strobe light at a disco. Between flashes, there are dark pauses lasting 26.9 nanoseconds (billionths of a second).

In the BESIII detector, particles put on a show: they collide, are born, and decay, leaving flashes of light. But sometimes an actor can leave the stage unnoticed — through a hidden door that cameras don't see. Physicists were looking for exactly such 'quiet' decays, when a particle turns into something invisible to the instruments.

Dark matter is five times more massive than ordinary matter, yet it emits no light. Its nature remains unknown. One candidate is the ultra-light axion particle. Axions could pierce right through the planet, barely noticing atoms.

Dark matter is an invisible substance that holds galaxies together but emits no light. Catching its particles is like trying to hear a whisper in a noisy hall. Ordinary detectors only pick up loud impacts, while weak signals get drowned out by background noise.

A fridge magnet holds on thanks to tiny internal arrows: each one like a miniature compass. If you hit the metal with an ultrashort flash of light, these arrows start to jitter chaotically, and magnetism melts away in a millionth of a billionth of a second. Previously, such 'melting' was too fast to observe.