afterglow

A beacon at the edge of the galaxy blinks without a schedule: sometimes silent for years, sometimes emitting hundreds of flares in a single day. Such a beacon needs a watchman who never sleeps and never gets distracted.

A gas target is like a funnel: the steeper its walls, the stronger the flow. But in this funnel, it is not water that flows, but ultraviolet light, born when a powerful laser pulse passes through a cloud of argon. The efficiency of this conversion is usually minuscule, about 0.001%: out of a thousand laser photons, only one turns into useful ultraviolet.

A particle with an energy of $$10^{18}$$ eV hitting Earth's atmosphere is like a tennis ball traveling at 200 km/h slamming into a wall. Astrophysicists have debated for decades where such projectiles come from. Gamma-ray bursts, brief and powerful explosions of gamma radiation, have long been suspected as accelerators.

The mirror races along at nearly forty thousand kilometers per second. Light that strikes it bounces back, but changed, like a ball volleyed by a racket in mid-swing. That's exactly the kind of mirror scientists have built inside an ultra-thin glass thread filled with hydrogen. First, a powerful laser pulse is sent down the fiber.

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.

An avalanche in a sandpile starts with a single grain. No one knows exactly where it will slip or how big the slide will be. But if you keep pouring sand, the pile itself reaches a state where avalanches of all sizes, from tiny trickles to massive collapses, follow the same law.

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.

Dark matter is the invisible scaffolding of the universe. It's there, we know from the motion of stars and galaxies, but what this scaffolding is made of remains unknown. One guess is ultra-light particles similar to axions. They barely interact with ordinary matter, yet occasionally they do get involved.

The first moments after the big bang: space expands rapidly — physicists call this period inflation. Inside this swelling fabric, like soap bubbles in a stream of air, regions of new vacuum begin to form — a first-order phase transition. Most bubbles pop or merge as soon as they appear.

The mystery of antimatter in space has long puzzled astrophysicists: where do positrons come from, settling like snowflakes into our detectors? The answer might lurk in the most ubiquitous gamma-ray background. The Universe is soaked in diffuse light — the cosmic photon background (CPB).

In the depths of the Universe, when a massive star collapses into a black hole or a magnetar is born, a gamma-ray burst flares up — for an instant, it outshines all the stars in the observable Universe.

The cosmos is full of screams we can't hear. Every time a black hole tears a star apart, a blinding flash is born, and often — a narrow relativistic jet, shooting out thousands of light-years. But if that searchlight is aimed away from Earth, we see only a faint afterglow — a radio echo arriving with a delay.

Two neutron stars spiral closer and collide. The result: a gravitational wave, a ripple in spacetime, a short gamma-ray burst, and a faint glow astronomers call a kilonova. But sometimes the signal passes by a massive galaxy.

Two neutron stars, ultra-dense remnants of massive stars, merge into one, and the space around them shudders: a gravitational wave is born, a ripple in the very fabric of spacetime. Almost simultaneously, a narrow stream of matter, the jet, erupts from the scene.

A lighthouse sends its beam through a storm of its own mirrors: that's roughly how fast radio bursts behave when trying to leave a magnetar's vicinity. A magnetar is a neutron star with a magnetic field a quadrillion times stronger than Earth's.

Blazars are long-lasting beams from black holes at the centers of galaxies. Gamma-ray bursts are the briefest flashes from supernova explosions or neutron star mergers. The former act like eternal spotlights, the latter like camera flashes.

Moments before totality, swift shadow bands glide across the ground, like ripples from pebbles tossed into water. For centuries, this phenomenon baffled scientists. It turns out the key is that light is a wave. The Sun isn't a pinpoint lamp but a vast disk. When the Moon nearly covers it, a thin glowing crescent remains.

Light passes through a crumpled film — and comes out slightly altered. In much the same way, gravitational waves born in the early universe feel the lumpy distribution of galaxies and dark matter.

A shockwave erupts from the star's surface, and for a brief moment, a blinding flash of ultraviolet and X-rays is born. This very event, named EP260321a, was spotted by the Einstein space telescope in March 2026. The light took about 450 million years to reach Earth.

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.

A black hole is a cosmic pocket into which everything, even light, falls. But the pioneering work of John Wheeler, Stephen Hawking, and Roger Penrose showed: sometimes, due to the colossal spacetime curvature, the pocket turns inside out.

A giant drum has just taken a hit. Its membrane is still trembling, but besides the main boom, a fine ripple spreads across it — someone ran a finger over the taut skin. In much the same way, in the first moments after the Big Bang, spacetime vibrated not only with the "roar" of expansion but also with the tension of suddenly emerging magnetic fields.

A flashlight doesn't cast a uniform circle of light; it has a bright spot in the center and a blurred halo at the edges. If you switch it off quickly, the edges are the last to fade, and by how the light dies, you can guess the shape of the reflector.

In 2017, detectors picked up a tremor in space — gravitational waves from the merger of two neutron stars. At the same moment, telescopes saw a flash. For the first time, one event spoke in two languages at once: light and gravity.

The center of the Milky Way has long puzzled astronomers: around the supermassive black hole Sagittarius A* there are more gamma rays than expected.

A black hole collision isn't just a burst of gravitational waves; it also leaves a lasting trace: an eternal curvature of spacetime — gravitational memory. Like a boat on water leaves a lingering wake, the cosmos 'remembers' the catastrophe.

At the very heart of the Milky Way, something is glowing, but not with starlight; with gamma rays invisible to the eye.

Radio waves from a gamma-ray burst — the cataclysmic death of a massive star whose flash briefly outshines an entire galaxy — reach Earth polarized. This means their electric field oscillates predominantly in a single plane, like a compass needle frozen in a magnetic field.

A translator gets distracted by every rustle in the hall, and a one-hour meeting stretches into two. Gluons, the particles that carry the strong force inside protons, behave much the same way. Usually, they dart back and forth, holding quarks together.

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 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 gamma-ray burst is like a shot from a cosmic cannon. First a brief flash of light, then a fading afterglow. But inside that flash, things aren't so simple: its color and brightness don't change at the same time.

In a distant galaxy, at a distance that light takes 11 billion years to cross, something flashed. The Einstein Probe X-ray telescope caught a brief, needle-prick-like burst: it lasted only a few dozen seconds.

An ordinary camera flash lingers for hundredths of a second, but for atoms, that's an eternity. Inside molecules, electrons jump in attoseconds: billionths of a billionth of a second. To capture that, you need a light pulse shorter than the event itself. Physicists take an electron beam in a linear accelerator and compress it so that individual bunches become thinner than a hair — in time.

Gamma-ray burst GRB 221009A flared so brightly that it was dubbed the 'brightest of all time.' The LHAASO observatory detected gamma rays from it with energies up to 13 TeV — thousands of times more energetic than particles in an X-ray machine.

A gamma-ray burst is a brief but extremely powerful flash of light, born from the merger of neutron stars or the collapse of a massive star. Inside such a flash, plasma flows race at enormous speeds and collide with each other.

The Fermi telescope spent 17 years recording gamma rays from the active nuclei of galaxies with giant black holes at their centers. The glow of their jets resembles a chaotic cacophony: it constantly changes.

In 2017, the IceCube detector caught a neutrino from the distant galaxy TXS 0506+056. It was like hearing a phone ring from across the ocean: the signal came from where the most energetic particles in the Universe are born. At the same time as the neutrino, astronomers spotted a gamma-ray flare, and two to three years later, radio waves. Why was the radio late?

When a massive star dies, a supernova explosion occurs, so powerful that a single flash outshines an entire galaxy. In this fire, billions of axions are born — invisible particles that leave almost no trace. Every second, trillions of these tiny things fly right through each of us, completely unnoticed.

Massive stars end their lives in a colossal explosion, which Fritz Zwicky called a supernova. The core crushes down into a black hole or a neutron star.