ultraviolet radiation

The camera captures not a race but a dance of atoms. In vanadium dioxide, the transition from an insulating to a metallic state occurs within trillionths of a second, yet until now no one had seen exactly how the vanadium and oxygen atoms move. Now, ultrafast electron diffraction has captured this route frame by frame.

Twelve stars have received X-ray passports. Now, for each of them, we know the exact radiation dose received by a planet in the habitable zone, the region where liquid water is possible.

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.

After a nuclear explosion, soot rises into the sky. It settles high above the clouds, in the stratosphere, and stays there for years. This soot acts like a thick curtain: it blocks some sunlight and alters the chemistry of the sky.

High-frequency sound focused on a single point acts like an invisible lens gathering sunlight. Inside a tumor, such a lens can raise the temperature to about 72°C in a second, like hot water from a tap, but inside living tissue. Meanwhile, surrounding healthy cells remain almost untouched.

A camera flash that fires in a thousandth of a second doesn't heat the subject — unlike a regular flash that lasts a full second. A similar trick has been found in radiotherapy: when a radiation dose is delivered in milliseconds instead of minutes, healthy tissues suffer less. This is called the FLASH effect.

Imagine an artist whose canvas is an entire planet, and whose palette is molecules drinking starlight. His brush is billions of years of evolution, and his painting is a spectral portrait visible even from another star system.

Within a field of view the size of a grain of sand held up to the eye, hundreds of galaxies lie hidden, smeared into arcs by the massive cluster Abell S1063.

Dark matter is the invisible scaffold that holds galaxies together. But how did it come to be? The standard answer: particles of dark matter once stopped colliding and "froze out" in the amount we see today. However, there's a trickier path — UFO, or ultra-fast freeze-out. Here, everything is like coffee that cools down and then heats up again as you carry it through a cold corridor.

A massive star ends its life in a spectacular collapse: the core compresses into a neutron star or a black hole, while the outer layers fly off in a dazzling supernova.

The solar corona (the outer atmosphere of the Солнца, heated to millions of degrees) glows in ultraviolet light, but these rays are absorbed by the air and never reach Earth. Direct images of the corona from space have only been available since the 1990s.

Elliptical galaxies are quiet stellar metropolises in retirement. By all rights, their light should be calm, reddish, like a sunset. But their spectra scream otherwise: in the far ultraviolet, these old-timers blaze like holiday lights. For three decades, astronomers have puzzled over this 'ultraviolet upturn' (UV upturn).

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.

When astronomers peer at distant worlds, they often don't see crisp lines of water vapor or methane, but a blurry silhouette, as if the planet has thrown on a thick veil. This veil, a haze of organic particles, behaves like a temperamental photographic plate: it darkens under harsh ultraviolet light, revealing hidden chemical patterns.

When the James Webb Space Telescope turned its gaze deep into time, astronomers expected to see familiar galaxies. Instead, the images were dotted with a scattering of bright, incredibly compact red dots.

Images from the James Webb Space Telescope have revealed unexpectedly intense light from the first galaxies — colossal star systems that formed shortly after the Big Bang. Imagine a toaster browning a slice of bread in a minute, while an oven takes an hour to bake a loaf — the result is essentially the same.

Neutron stars are the ultra-dense remnants of stars, where matter is compressed to the limit described by Subrahmanyan Chandrasekhar. Magnetars are a type of neutron star with a magnetic field a quadrillion times stronger than Earth's.

Frozen cake batter is dotted with tiny raisins. If the batter is uniform, all the raisins will puff up evenly, and the cake will be smooth. But if the batter has denser spots (some sweeter, some more bland) the raisins will be distributed unevenly: dense in some places, sparse in others.

A dim lightbulb suddenly starts illuminating patterns on the wall that were invisible to the eye. That's roughly how astronomers look at distant dwarf galaxies — tiny stellar islands poor in heavy elements. In some of them, a faint violet glow of ionized helium has been spotted (a specific spectral line He II 4686 Å).

A pendulum swings with such precision that, had it been counting seconds since the Big Bang, it would have drifted by only half a second by today. That is the stability of the new portable ultraviolet laser — the heart of aluminum atomic clocks.

A detector filled with superfluid helium-4 is like a perfectly still lake. The liquid doesn't slosh or bubble: it's frozen in a single quantum state. An invisible guest, a dark matter particle, flies through it. It doesn't shine or leave a track. But sometimes it nudges a helium nucleus.

At the center of many galaxies sits a supermassive black hole. When gas falls onto it, the gas heats up and shines brighter than an entire galaxy: this is an active galactic nucleus. Sometimes a true hurricane erupts from there: a stream of ionized gas racing at tens of percent of the speed of light.

A film of aluminum nitride, as thin as a soap bubble, hangs above a mirror with a micrometer-sized air gap between them. When invisible infrared light with a wavelength of about 15 micrometers hits it, the film starts to vibrate in sync with the light, like a string that responds only to its own note.

A sunspot, a dark island on the scorching surface, breathes. Every three minutes, a wave spreads from it, runs along an invisible magnetic arch, and makes the plasma above a neighboring spot flare with a radio signal. Radio telescopes caught seven such flares in a row on February 14, 2024.

A laser beam as faint as a whisper of light has stirred a thorium-229 nucleus into a higher energy state. Most nuclei demand a blast of energy, but thorium-229 has such a tiny energy gap that even this gentle nudge works.

In a dark room, a flashlight only illuminates what falls within its beam. That's roughly how physicists study atoms: a short flash of light knocks out electrons, and by tracking their paths, you can figure out how the atom is built. But helium has states that don't fall into the ordinary 'beam'—they hide in the shadows.

A sheet of graphene is a mesh of carbon atoms one atom thick. Even the slightest contamination shows up on it, like dust specks on eyeglass lenses. Ten years ago, researchers learned to hide graphene between layers of boron nitride, like placing a fragile sheet between two pieces of plastic wrap.

At night in a dark room, the human body emits a barely perceptible glow. This light is so faint that only highly sensitive detectors can catch it. Some researchers thought this glow from the head could tell us about brain activity — no scanners or wires needed. But when put to the test, the story changed.

Water isn't the only thing life needs. To assemble the first RNA-like chains from simple molecules, you need ultraviolet light, like the sunlight that helps plants, but harsher and with shorter wavelengths. Big stars like the Sun emit plenty of this light. Small, dim stars, however, have almost none: they shine mostly in red and infrared, like a glowing ember.

A shock wave in the Sun's corona is like the sonic boom from an airplane, except instead of air there is scorching plasma, and instead of sound there is a jump in density and magnetic field. On March 10, 2024, such a wave swept across the western part of the solar disk.

Light from distant stars, as it travels through cosmic dust, loses some of its energy. Dust grains absorb and scatter light, and the way they do so at different wavelengths reveals their composition and size. Astronomers call this the dust extinction curve.

Molecules in a solution behave like a crowd in a square: they can jostle randomly or line up in neat rows. An aqueous solution of disodium cromoglycate is a well-known model for chromonic liquid crystals, where such 'rows' form spontaneously. But if you shine ultraviolet light on the solution, order collapses: molecules start breaking apart.

Two cities: one with neat, straight streets, the other with a tangle of alleys. If you send a powerful flood of water through both, in the first the water quickly drains away through channels, while in the second it swamps everything. That's roughly how tissues behave under ultrafast radiation therapy, known as FLASH.

A green flashlight beam dives into a pool and reaches the bottom with barely any loss. Water is transparent to green light, which is why it's used for underwater communication. But to send video or sensor data, the light needs to be switched on and off very quickly — billions of times per second. Ordinary lasers are too slow and unstable for this.

A giant cosmic funnel sucks in gas from its surroundings. But not all of that gas falls in — some is spat back out, like splashes from boiling water. That's exactly what the ultraluminous X-ray source NGC 5204 X-1 does: a compact object (likely a black hole) feeds so voraciously that the excess escapes in powerful jets.

The night sky is no longer as quiet as it used to be. Thousands of satellites are whizzing overhead, and each one can accidentally emit radio waves, interfering with astronomers trying to listen to distant galaxies. To make sense of this noise, scientists pointed the 21CMA radio telescope in China at Starlink satellite passes.

Ordinary white light is a jumble of all colors at once, like the noise of a crowd where everyone speaks at their own frequency. But scientists need light where frequencies are aligned with ruler-like precision, like piano keys, where each note sounds distinct and exact.

Radiation therapy is like shooting at a small target with a very large-caliber rifle: even a precise shot hits a large area around it. The thickness of the 'trace'—called the penumbra — is 2–3 millimeters in standard machines. For a tumor in the lung, that's not a big deal, but next to a nerve or a blood vessel, those millimeters decide whether a person stays healthy.

Light we can't see but feel as heat turns out to be the key to cellular life. A new type of microscope uses waves 2000–2500 nanometers long, three times longer than red light, and such waves barely scatter in tissue. Thanks to this, the device peers into a tumor spheroid like a flashlight through frosted glass, illuminating individual molecules.

At the centers of many galaxies lurk supermassive black holes. From time to time they 'scream' — unleashing powerful X-ray flares. Scientists have long puzzled over the nature of these 'quasi-periodic eruptions'.