X-ray radiation

A globe sits on a table, and a ruler lies beside it: one is curved, the other straight. X-ray telescopes have lived with this mismatch for years. Their mirrors gather light onto a curved surface, like the globe, while the detectors that catch that light have been flat, like the ruler.

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.

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.

Light born when a fast electron enters a material is usually assumed to be the same in all directions. But in crystals where optical properties depend on direction, that's not the case. Run your hand over velvet: one way it's smooth and shiny, the other — dark and rough. Similarly, a crystal responds differently to light depending on how it's oriented.

Light that never reaches the camera still leaves its mark on it. That's how the new imaging method works: you illuminate the object with one color, and the picture is assembled from another. Inside the crystal, light waves mix, and information about the invisible transfers to a visible beam. In the experiment, they used a silver thiogallate crystal.

A laser beam strikes a thin target hidden inside layers of another material. Within billionths of a second, the material is compressed to a density of 25 grams per cubic centimeter, as if a piece of lead became more than twice as heavy without moving an inch.

The XMM-Newton X-ray telescope stared at galaxy Mrk 1044 for two straight hours. Inside it, a black hole is surrounded by a swirling disk of superheated gas. This gas glows in X-rays, and its light flickers — brighter, then dimmer. For the first half hour, the flickering of soft and hard X-rays was in step.

When a laser beam hits a gas, it tears electrons from atoms and accelerates them to nearly the speed of light. As these electrons fly through the plasma, they emit X-rays, like a glowing trail from a fast particle. In the new work, physicists made a single laser pulse create not one but two such trails in succession.

When a laser beam hits a gas, it tears electrons from atoms and accelerates them to nearly the speed of light. As these electrons fly through the plasma, they emit X-rays, like a glowing trail from a fast particle. In the new work, physicists made a single laser pulse create not one but two such trails in succession.

On the surface of the Moon and asteroids, you can find pits smaller than a pinhead but with shiny, melted rims. Such marks are left by tiny meteorites, but the exact impact speed at which melting occurs remained unclear.

A shooter aims at a target, pulls the trigger, and hears two shots: one loud, one quiet. That's how the new setup works, except instead of bullets, there's an electron bunch, and instead of shots, there are two flashes of light. One flash is X-ray, the other is terahertz. They fly to the same point with perfect timing.

In July 1969, as Apollo 11 flew toward the Moon, astronauts noticed something unusual: brief flashes of light that appeared even with their eyes closed. At first, this was attributed to fatigue, but the flashes recurred in different crews. Gradually, it became clear: cosmic rays were to blame — tiny particles hurtling through space at tremendous speeds.

A shipping container is a steel safe the size of a room, packed with goods. X-rays struggle to see through it: thick walls and dense cargo block the rays. Enter muons — particles born high in the sky that constantly rain down on Earth. They can pass through even lead, but they veer slightly off course when they encounter something heavy.

The hot gas in galaxy clusters shines in X-rays, and a significant portion of that light comes from iron atoms that have lost many electrons. These atoms leave characteristic bright lines in the spectrum, like fingerprints. Astronomers use them to determine the temperature, density, and motion of the gas.

An X-ray flash tears through matter in billionths of a second. To remember it, physicists make atoms briefly absorb the light and then release it back. But pulling out a photon on command is like grabbing the right book from a shelf when the shelves move on their own. The usual approach is to move several absorbers with extreme precision, like a well-coordinated orchestra.

Boiling milk develops a trembling skin. By watching its movements, you can guess the strength of the fire beneath the pot and the fat content of the milk. In a similar way, astrophysicists peer into the ancient microwave radiation — the oldest light that has reached us from an era when the universe was only 380,000 years old.

A cosmic "caliper" will soon measure a neutron star to within a hundred meters. For an object a couple dozen kilometers across, that's like measuring the thickness of a human hair from a kilometer away. A neutron star is the remnant of an exploded supernova.

In the distant Cigar Galaxy, there is an unusual beacon. It doesn't shine in the usual sense: its rays are born in a scorching cloud around a black hole that is devouring matter from a companion star. Such objects are called ultraluminous X-ray sources. Their X-ray brilliance is so intense that it outshines entire galaxies. This cloud, the corona, is like a boiling cauldron.

At the centers of many galaxies lurk giant black holes. They are surrounded by dense clouds of hot plasma that emit a powerful X-ray glow.

In June 2024, the CHIME radio telescope recorded over 700 radio bursts per hour from source FRB 20240114A. Such a hyperactive repeater releases in one hour nearly all the magnetic energy of a typical magnetar (a neutron star with an ultra-strong field).

The event horizon's edge is never calm. Quantum vacuum boils there, and particles sometimes burst out of this foam: that is how Stephen Hawking in 1974 discovered black hole radiation, forever linking gravity with quantum field theory.

A waterfall that doesn't heat up from the fall but freezes — that's roughly how gas behaves as it flows onto a neutron star in an X-ray pulsar when the star shines dimly. Usually, infalling matter is heated to a white-hot glow, but new work shows the opposite.

For years, silence reigned in the heart of galaxy 1ES 1927+654: the accreting gas merely whispered in X-rays, leaking slow winds. But in 2022–2025, the picture changed dramatically. Spectra taken by XMM-Newton and Swift lit up with emission lines — a narrow peak at 0.56 keV, likely from OVII oxygen, a broader feature near 1 keV, and a powerful iron band in the 6–7 keV region.

When two neutron stars, the ultra-dense cores of dead stars, collide, a kilonova is born: an explosion a thousand times brighter than a typical nova. This is the universe's true smelting works. In the scorching cloud racing outward at near-light speeds, a furious flux of neutrons transmutes atomic nuclei into gold, platinum, osmium.

The enigma of fast radio bursts (FRBs) is not just a question of 'what exploded?' It’s a drama of energy transfer under extreme conditions, where the slightest stumble leads to collapse.

An ordinary microscope is powerless when you need to examine a single virus in detail. It's too small. But there's a tool that fires flashes billions of times brighter than sunlight — an X-ray free-electron laser. It's designed to 'photograph' a particle before the beam vaporizes it.

A pot of porridge boiling over a high flame: bubbles carry grains from the bottom to the surface. A similar mechanism works on a neutron star. As it accumulates hydrogen and helium from a companion star, it occasionally triggers a powerful nuclear explosion — an X-ray burst.

A powerful laser strikes a diamond like a sledgehammer, with matter itself serving as the anvil. The impact lasts only an instant but generates pressures a million times greater than atmospheric. Physicists have long dreamed of peering into that moment to see how atoms rearrange under the onslaught. The X-ray beam here is like a camera flash.

Dark matter detectors are essentially incredibly sensitive microphones, capable of hearing a whisper amid the roar of a rock concert. Their job is to catch the rare nudges from hypothetical dark matter particles, which are thought to occasionally collide with atomic nuclei of ordinary 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.

A pebble drops into a pond, and ripples spread across the water. But one wave suddenly doesn't spread out: it clings to an invisible fold on the surface and runs only along it.

A fire hose blasts into a snowdrift. The water doesn't just shove the snow aside — at the point of impact, spray, steam, and a roar are born. That's roughly how jets behave: narrow streams of matter shooting out from around a black hole at enormous speeds.

Gravitational waves are ripples in the very fabric of spacetime, akin to vibrations of a giant cosmic string. Conventional detectors like LIGO and Virgo pick up low-frequency "notes"—disturbances from mergers of massive black holes of stellar masses.

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.

Gravitational waves — the cosmic tremors from distant cataclysms — are so faint that detecting them is like trying to hear a whisper in a hurricane. But a black hole can amplify that whisper many times over.

In astrophysics, some numbers seem random yet recur with the persistence of a spell. One such number is the ratio of X-ray brightness to H-alpha hydrogen emission in turbulent gas tails. From galactic winds to ‘jellyfish’ slicing through clusters, this ratio steadily holds at around three.

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.

In astrophysics, some numbers seem random yet recur with the persistence of a spell. One such number is the ratio of X-ray brightness to H-alpha hydrogen emission in turbulent gas tails. From galactic winds to ‘jellyfish’ slicing through clusters, this ratio steadily holds at around three.

When an electric charge moves with acceleration, it emits electromagnetic radiation, i.e., light — a familiar phenomenon in physics. However, researchers have found that when moving along a specially chosen trajectory, the radiation acquires unusual properties.