quasi periodic oscillation

Every five hours in the binary system IPHAS J190812.63+045728.1, one star completely hides the other. For 18 minutes, the white dwarf and its scorching disk vanish from sight, leaving only a modest red neighbor in the dark. This is a natural shutter that switches off the spotlight to reveal what usually hides in its glare.

In 2015, the LIGO detectors caught the first ripple of spacetime from a black hole merger. Since then, hundreds of such events have piled up, each carrying the imprint of its ancestry: whether the holes were born together from a single pair of stars or met by chance in a dense cluster. The difference shows in the direction of their spin axes.

A black hole paired with a star works like a pump: it pulls gas from its companion, swirls it into a glowing disk, and occasionally ejects some of that matter in two narrow jets. In 2021, the system 4U 1543-475 put on such a show.

The cosmic detective story began with a quiet flash in the optical band. AT2019wzc slowly brightened and faded like a smoldering ember. But hidden inside was something more energetic — repeating soft X-ray bursts that astronomers call quasi-periodic eruptions. These eruptions last minutes to hours and repeat every few hours or days.

You could send a short radio pulse toward a black hole and wait for the reflected echo. Intuitively, the shorter the signal, the better it would probe the finest details of spacetime right at the horizon: that region from which even light cannot return.

A black hole is not silent. When perturbed, it rings like a bell, and that ring is its quasinormal modes — damped oscillations. Physicists delved into the world of charged black holes in anti-de Sitter space (a universe with negative curvature, like a saddle).

Try to pick out the rhythm of a distant drum through the noise of a construction site. Standard methods look for a steady "tick-tock-tick," but if the drummer plays erratically, with sharp hits and pauses, they might miss it entirely. That's roughly how astronomers searched for periodic signals in the emission of blazars — active nuclei of distant galaxies that shoot powerful jets of particles toward us.

May 2022. The space polarimeter IXPE, the spectroscope NuSTAR, and the monitor NICER simultaneously stared at one spot in the sky — at the black hole in the Cygnus X-1 system, where it orbits a blue supergiant in a close binary system with a period of 5.6 days.

After a hit, a black hole rings like a bell. But instead of sound, it emits gravitational waves whose frequency rapidly decays: these are called quasinormal modes. From such a 'ring,' you can infer the hole's mass, spin, and other properties.

The spiral of water draining into a sink spins faster and faster toward the center. In an ordinary black hole, that funnel ends in an infinitely sharp point — a singularity where the laws of physics break down. But this new work considers a different picture: the funnel doesn't taper to a needle but ends in a smooth, swelling bubble.

Space is full of invisible waves — ripples in the fabric of spacetime left behind by cataclysms like black hole mergers. An ordinary black hole swallows everything without a trace. But there are hypothetical exotic objects — ultradense clumps of matter without an event horizon (a surface from which not even light can escape).

A mosaic of squares and triangles covers the floor without gaps, yet it never settles into a simple repeating pattern. Such a pattern is a quasicrystal — a solid where atoms are arranged not periodically but according to a pattern of several waves of different lengths. These waves are incommensurate with each other, and together they create long-range order.

A black hole merger is not a silent impact. The newborn hole quivers and decays, emitting gravitational waves — ripples in space itself. This signal is called the 'ringdown,' and it resembles the fading chime of a bell: it has a fundamental tone and several overtones.

Hot gas spirals inward, falling onto an invisible superdense object. Such a disk resembles a giant whirlpool, but it is often tilted: its axis does not align with the rotation axis of the central body. The gravity of the massive object makes the disk wobble slightly, like a spinning top losing its balance.

The NICER X-ray telescope has become a precise stethoscope for astrophysicists. In 2025, it was 'listening to' the black hole in the binary system 4U 1630−47—a compact object born from the core collapse of a massive star (the stability limit for white dwarfs was…

The mergers of black holes, first predicted by Karl Schwarzschild, are the main source of gravitational waves picked up by LIGO detectors. Over the years, 259 events have accumulated, each one an encrypted birth story of a pair. But is there a hidden system in this data?

A black hole is not a dead object. After a disturbance, such as merging with another hole, it rings like a bell. This ring is not just a sound but a complex set of damped oscillations called quasinormal modes. Their frequency and damping rate depend on the hole itself: its mass, charge, and spin.

In the centers of distant galaxies, X-ray 'beacons' sometimes light up. They don't flash randomly but on a strict schedule: every few hours or days. These bursts are called quasi-periodic eruptions (repeating at nearly regular intervals).

The heart of many galaxies is a supermassive black hole. It doesn't just sit at the center; it occasionally flares brightly as it swallows surrounding gas.

A black hole rings like a bell when something massive falls into it. This ring is gravitational waves, and its overtones tell us about the shape of the horizon.

Waves sort pebbles on a sandy beach. Small stones lie close together, nearly identical in size. Farther from shore, there's a scatter of larger and more varied ones. And right at the waterline, where the surf is strongest, the biggest and most rounded fragments pile up. Nature sorts black holes by mass in much the same way when they merge in pairs.

Gravitational waves from a tiny body falling into a black hole work like an X-ray image. Only instead of a bone, they illuminate the curved spacetime itself.

Drop a pebble into a pond, and ripples spread across the water. A black hole 'sounds' much the same when matter falls into it or when its spacetime gets a gentle jolt. These fading oscillations are called quasinormal modes, like the tolling of a bell that gradually fades away.

A black hole is like a bottomless well. You can measure how much water has flowed into it by watching the level from outside. But how do you find the mass of the water itself if you're standing inside the well? That's roughly the problem the authors of a new paper tackle.

A black hole can be compared to a bell: after being struck, it vibrates, emitting a decaying 'ring.' This ring is the gravitational waves that detectors on Earth pick up.

A giant black hole tore apart a star, leaving behind a lopsided disk of scorching gas — like a vinyl record warped by the heat. Now a tiny black hole (or a star) zips around and repeatedly pierces that disk. Each puncture is a bright X-ray flare.

Strike a bell, and it rings. But the sound isn't arbitrary: the bell itself picks out the notes to which its metal is tuned. It turns out a black hole behaves the same way. When something falls into it, or its spacetime gets warped, it starts to oscillate.

Two figure skaters glide on the ice. One is light and cautious, barely rotating. The other is massive and fast, spinning with all its might, and in different directions at that. That's roughly the picture painted by gravitational waves from black hole mergers.

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.

Sound travels through a medium at a certain speed. If the medium moves faster, the sound gets swept along by the flow — like a wood chip pulled into a whirlpool. In superfluid helium — a frictionless liquid — rapid rotation spawns vortex funnels. Inside them, an acoustic black hole forms: a region from which sound cannot return.

The shadows of supermassive objects at the centers of galaxies, M87 and the Milky Way, have become icons of modern astrophysics. But what if these shadows are not from absorption, but passage? The equations of Einstein allow for traversable wormholes — tunnels in the fabric of spacetime.

Strike a bell, and it responds with its own note. Likewise, a black hole disturbed by the fall of a star or another black hole begins to 'ring,' emitting gravitational waves. But instead of sound, it's the trembling of space itself, and instead of a single note, a whole set of decaying frequencies. These are called quasinormal modes.

A black hole, perturbed by a merger, vibrates at characteristic resonant frequencies — much like a bell ringing after being struck. Each hole has its own spectrum of these oscillations, allowing astronomers to reconstruct its parameters.

At the heart of galaxy 1ES 1927+654, a black hole behaves like a lighthouse with a faulty mechanism. Every six and a half minutes, it releases a burst of X-ray light, a rhythm astronomers have been tracking since 2022. At first, the beacon's tempo wandered — speeding up and slowing down, with intervals ranging from one beat every eighteen minutes to one every seven.

At the center of galaxy PDS 456 shines a quasar — a black hole devouring gas that glows brighter than hundreds of billions of stars. The X-ray telescope XRISM peered into this light and saw a picket fence of dark bands, like shadows cast by a fence at sunset.

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.

A spinning top on a table wobbles: its axis is tilted, and the motion becomes unsteady. Black holes surrounded by a disk of gas and dust behave similarly. If the rotation axes of the black hole and the disk do not align, the whole system begins to vibrate, producing ripples in spacetime — gravitational waves.

The black hole Swift J1727.8-1613 emits X-ray bursts in a strict rhythm — like a cosmic heart. Gas falling onto the hole forms a spinning disk, and its glow pulsates. A Chinese telescope picked up this rhythm, like a stethoscope catching a heartbeat.

During its 2021 outburst, the black hole in the GX 339-4 system behaved like an actress changing costumes between scenes. In the hard state, it wore two coronas at once: a hot, rarefied one, and over it, a warm, dense one. In the soft state, only the hot corona remained.

Drop a stone into a pond — the ripples spread and fade away. A black hole, after colliding with another hole or a star, also 'rings', but its oscillations are not simple. Near the hole, 'overtones' sound — secondary waves born from the nonlinearity of spacetime itself.