dysprosium

A hunter sets snares in the woods. They know the animal's habits but not whether it will ever show up. In much the same way, physicists set up detectors in hopes of catching particles of dark matter — the invisible substance thought to make up most of the Universe's mass. A new study offers hunters an unusual tool: not a trap, but a measuring tape.

A star's radius drops by a thousand kilometers. Not because its mass increased, but because its own magnetic field squeezed the crust like an invisible corset.

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.

Two hundred and eighty-nine days: that's how long one rotation of the white dwarf white dwarf WD 1532+129 takes. This is not just a record: on its surface, near the magnetic poles, scars of iron and other metals appear — silent testimony to planets it has devoured.

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.

A tuning fork struck once rings pure and long. But if you shake the fork itself while it sounds, the tone wavers and dies out quickly. Something similar happens to electrons in any piece of matter. Atoms in a lattice never stay put: thermal vibrations keep them jittering.

An inflatable balloon with magnetic field lines drawn on it with a marker is a simple model of how a weak magnetic field behaves in an expanding universe. While the balloon is small, the lines lie obediently on the rubber and don't hinder its stretching. That's roughly how a field fills ready-made space without arguing with its geometry.

A teaspoon of neutron star matter weighs as much as a mountain. But this mountain may have an invisible twin. Deep inside a neutron star, ordinary matter is compressed to unimaginable densities. There, protons and neutrons can dissolve into a quark soup.

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.

A billiard ball slams into another. Impact, and the balls scatter. But if the push is not sharp but very gentle, the balls just roll together without bouncing. An atom behaves much the same way when hit by a dark matter particle.

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.

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.

Deep underground in Japan, a huge tank of ultrapure water waits for rare visitors — neutrinos arriving from distant stellar explosions. Such guests are few and far between: over years of observation, Super-Kamiokande registers only a handful of events.

A thick rubber band is twisted tighter and tighter. At some point, it can't take it anymore — it snaps and whips around, releasing the stored energy. That's roughly how magnetic fields inside neutron stars — the ultra-dense remnants of exploded stars — behave.

In the first moments after the Big Bang, the universe was a boiling soup of elementary particles. Even the light neutrinos were actively colliding with everything around. But the rapid expansion cooled this soup, and the neutrinos broke free, becoming almost indifferent to the surrounding world.

Dark matter has eluded direct observation so far, even though its gravity holds galaxies together. One hypothesis: it’s made of axions — ultra-light particles predicted by theory.

If you toss a handful of coins onto a table, they land in a jumble. But in some crystals, atoms arrange themselves into a pattern reminiscent of a woven basket — the kagome lattice. In the metal MgMn₆Sn₆, manganese atoms form such a lattice, and at room temperature they act like tiny magnetic needles.

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 the first moments after the Big Bang, the universe was not empty and quiet but filled with hot plasma, particles, and magnetic fields. Among the particles, there may have been axions — light, nearly elusive dark matter candidates.

A tiny superconductor, levitating above a magnet, is like a cork on the surface of an invisible ocean. The slightest breath of dark matter makes it shudder. Scientists examined two kinds of such 'wind'. The first – gravitational waves, which stretch and squeeze space itself, like ripples on the fabric of the cosmos.

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 crystal Co2SeO3Cl2 resembles a layered cake, with each layer being a buckled honeycomb grid of cobalt atoms. When cooled to 25.4 K (−247.75 °C), the magnetic moments of the atoms begin to align like compass needles, but not all at once — rather in four steps, at 25.4, 16.8, 11, and 3 K. Each step brings a new pattern of magnetic order.

A lithium cobalt phosphate crystal resembles a chessboard, where the black and white squares are regions with opposite directions of the magnetic moments of cobalt ions. These regions are called antiferromagnetic domains, and until now they have been hard to see: conventional methods required complex equipment or damaged the sample.

The nucleus of deuterium, or the deuteron, can be pictured as a microscopic spinning top. If its charge distribution is not perfectly symmetric, then in an external electric field this top experiences a minuscule tilt of its spin axis.

A magnet that stacks up like a pile of pancakes: that's how the material CrSBr is structured. At low temperatures, each layer is magnetized, but neighboring layers point in opposite directions, and their magnetic fields cancel each other out. This order is called antiferromagnetic, and it's fragile: just a slight warming demagnetizes the layers.

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 tiny magnet made of layers of sulfur, chromium, and bromine sits on a microscope stage. Inside it, like unexpected guests, sit erbium atoms — a rare-earth metal. These atoms can glow when hit with a laser, and their light tells us what's happening around them.

When cooled to -272°C, the Fe₄Nb₂O₉ crystal turns into a magnetic pattern where atomic arrows don't line up in a single row but fan out. It's like a crowd frozen in place, but each person looks in their own direction rather than at the back of the neighbor's head.

Ancient lead that lay on the seafloor for two thousand years has become the heart of a detector searching for the most elusive substance in the universe. From it, researchers grew a transparent lead tungstate crystal weighing 13 grams and cooled it to near absolute zero.

Electrons in a metal are like a crowd in a subway: each on their own, but at the slightest push, everyone moves at once. Physicists call this collective oscillation of the electron gas a plasmon. In superconductors, these oscillations are especially important because they reveal how electrons interact with each other.

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).

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.

The enigma of dark matter was already studied by Fritz Zwicky and Vera Rubin. For decades, it was depicted as a cold, listless skeleton that only draws galaxies together.

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.

Dark matter is invisible, but according to calculations, it holds galaxies together. Catching its particles is like hearing a whisper in a noisy room. You need a material that responds loudly and noticeably to the slightest nudge. Molecular magnets could be such a material — substances where each molecule acts as an independent tiny magnet.

The tiny magnetic arrows inside a crystal of terbium-iridium oxide behave strangely: instead of lying along their preferred axis, they stand across it. This state fully forms when cooled to 1.5 Kelvin — colder than outer space. Researchers probed the crystal with neutrons and observed how these flipped arrows oscillate and exchange energy.

In the 1930s, Fritz Zwicky, observing the Coma cluster, noticed anomalously high galaxy velocities: their motion pointed to a huge hidden mass gravitationally binding the system.

A century ago, magnetic observatories recorded only the slow breathing of Earth's core. Today, their data have become hunting grounds for particle physics. At the Eskdalemuir Observatory in northern England, fluctuations of the magnetic field are recorded every hundredth of a second.

The temperature in a room drops by a few degrees while the refrigerator runs without a single moving compressor. Inside, there is no Freon, but a piece of metal that is alternately magnetized and demagnetized.