x ray spectrum

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.

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.

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.

A sponge slowly watered from a watering can gets soaked all the way through. But if you dump the same bucket of water on it all at once, the middle gets wet while the edges stay almost dry. That's roughly how a material with nonlinear absorption behaves: the more intense the flux, the more it gets stuck at the point of impact.

A galaxy is like a city: bright lights and dense buildings at the center, sparse lights and emptiness toward the outskirts. But if you watch how gas rotates in a galaxy's disk, you see that its speed barely drops at the edges. As if invisible neighborhoods keep the motion going. Astronomers have found a way to map this invisible city.

The beacon flares up and then nearly goes out, even though the lamp inside burns steadily. That is exactly what astronomers saw when they pointed their telescopes at the galaxy I Zwicky 1. At its center sits a supermassive black hole that devours gas and dust so greedily that a scorching disk forms around it, shining brighter than an entire galaxy.

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.

A lighthouse that changes the color of each flash in time with its rotation: that's one way to describe what astronomers saw when they pointed the latest X-ray telescope, XRISM, at the pulsar Hercules X-1. This object is a neutron star pulling matter from a companion ordinary star.

The crust of a neutron star is not just a solid shell. Under pressures of billions of tons per square centimeter, atoms lose their electrons, and the remaining nuclei arrange into a rigid crystal lattice, reminiscent of a honeycomb, but made of matter a trillion times denser than steel.

When matter is heated to millions of degrees, it turns into plasma — a mix of free electrons and ions, like a boiling soup of charged particles. You can't measure the temperature of such a 'soup' with an ordinary thermometer, but you can shine X-rays through it.

A galaxy is like a glowing pancake studded with stars. If you look at it face-on, you see everything at once — both the bright spiral arms and the dark dust lanes. But tilt the pancake, and the picture changes: layers overlap, light blends together. This very effect, it turns out, creates the illusion of a tight link between radio and gamma-ray emission in distant star systems.

An X-ray beam is a stream of tiny packets of energy, photons. Ordinary detectors count them but don't distinguish shades: two photons with close energies look the same to them. The new device works like a sensitive thermometer: it catches each photon and measures how much it warms a thin film. From the warming, you can tell exactly how much energy the photon brought.

The neutron star 4U 1735-44 is gobbling up matter from a companion star. The matter spirals into a flat disk, like water going down a bathtub drain. But this disk shines in X-rays, and astronomers have for the first time measured how "combed" those rays are: that is, how polarized.

At the center of the distant galaxy MCG-6-30-15 lies a supermassive black hole. Around it swirls a disk of incandescent gas, and above the disk hangs a cloud of even hotter particles — the corona. In February 2024, three X-ray telescopes (XRISM, NuSTAR, and XMM-Newton) observed this system simultaneously.

The center of our galaxy is a crowded kitchen where several dishes are simmering at once, and their steam blends into a single cloud. X-rays from the exploded star's remnant, from the stellar wind around the supermassive black hole, and from hot gas between stars all overlap.

The black hole MAXI J1810-222 behaves like a giant vacuum cleaner with a reverse valve: it pulls in matter, but some of it gets spat back out into space. This "backflow"—a stellar wind — had been spotted by astronomers before, but only as a blurry smudge in X-rays.

At the center of the Milky Way, among dense clouds of gas and dust, lies a region called Sagittarius C. It's like a bustling crossroads: stars are born here, streams of matter collide, and the whole scene is illuminated by X-rays. For a long time, this glow remained a mystery.

In the binary system 4U 1700-37, the massive supergiant star HD 153919 sheds a powerful stellar wind. This wind, like an invisible stream, rushes toward its compact companion — likely a neutron star. As it falls, the matter heats to millions of degrees and flares in X-rays.

When an X-ray burst erupts on a neutron star, its atmosphere heats up to millions of degrees. The light we catch with telescopes passes through this dense layer of gas, and gets dramatically altered along the way. The spectrum no longer looks like that of an ideal radiator: some colors get amplified, others dim.

For years, an X-ray telescope in orbit recorded how binary systems shine, where an ordinary star orbits a black hole or a neutron star. Matter from the companion falls onto the compact object, heats up to millions of degrees, and emits X-rays.