gravitational instability

At the center of an ultra-compact dwarf galaxy, a very dense stellar system spanning tens of light-years, there is a vacuum cleaner at work. But instead of dust, it sucks in gas shed by dying stars. This gas does not fly off in all directions; instead, it spirals into a funnel, a rotating disk that gradually settles onto the black hole.

A black hole is not just an abyss. It is a seething cauldron whose temperature rises as it evaporates. The authors of the study found that when the heat reaches a critical threshold, the hole seems to boil. It emits superheavy particles — the very ones that exist on a scale where any theory of gravity collapses.

A gas disk with a mass of four hundred thousand suns encircles the black hole at the center of the Milky Way. Its gravity works like a gravitational rudder: slowly but inexorably turning the orbits of binary stars, driving them into the region where tidal forces tear the pair apart.

89 milliseconds. That's how long a vortex avalanche lasts that abruptly speeds up the rotation of the Vela pulsar — one of the most famous 'glitching' pulsars. Pulsars are rapidly spinning neutron stars born in the collapse of supernovae.

A campfire burns steadily and long. But when the wind blows, the flame flickers out, leaving only embers. A similar story plays out with the gravastar — a hypothetical object that was supposed to replace the black hole. An ordinary black hole hides a singularity — a point where the laws of physics break down.

Inside planets and stars, in rotating oceans of plasma, turbulent flows, Coriolis forces, and magnetic tension collide. The central question is how the energy of this chaos crystallizes into a stable magnetic framework that can last billions of years.

A thick stew slowly cools in a pot. Suddenly, the flame beneath it flares up, and the stew begins to boil, breaking into many small whirlpools. Much the same happens to the disk of gas and dust around a young star when it experiences a flare — a sudden influx of matter from the disk onto the star.

Imagine a spinning top the size of a city, weighing more than the Sun and making hundreds of revolutions per second. That's a neutron star — the remnant of an exploded star. Occasionally, its rotation suddenly speeds up, as if something inside has switched. Astronomers call these jumps glitches and suspect that invisible vortices in the star's superfluid interior are to blame.

A figure skater pulls their arms in, and their spin suddenly accelerates. When a massive star exhausts its fuel and its core collapses, something similar happens, but on a cosmic scale. The core shrinks to a city-sized sphere, and if it is spinning rapidly, a peculiar instability can arise.

The cosmic accounting has hit a snag. The bookkeeper is balancing the books: in one column, all the planets astronomers have counted in the galaxy; in the other, the stockpile of building material in the dusty cocoons of newborn stars. The numbers don't line up. Even if you gathered every last grain of dust and molded it into planets, there wouldn't be enough material.

At the center of almost every large galaxy lurks something supermassive and dark. Most often, that something is thought to be a black hole — a region where gravity is so strong that even light cannot escape. But what if it's not a black hole, but a dense ball of ultralight particles — a boson star?

A huge rotating pancake of gas and dust surrounds a young star. In such a "maternity ward" for planets, rings and gaps are often seen, as if an invisible plow had carved furrows. These are usually attributed to already-formed planets that clear paths with their gravity.

River water often swirls into funnels. But in semiconductors, the foundation of microchips, electrons at low temperatures and high purity also turn into a fluid. If you create a circular cavity, vortices appear, just like in a river backwater.

After the Big Bang, dark matter and ordinary matter (mostly hydrogen) went their separate ways in terms of speed. Their gravitational pull acts like a bow gliding across a string: when frequencies match, resonance occurs, and sound waves start to rapidly grow in ordinary matter.

An old chest of family heirlooms opens, and inside lie jewels that were thought to be as old as great-grandmother. But suddenly it turns out: the gold was remelted, the stones were recut, and this happened much later than thought. A similar story happened to the oldest particles in meteorites — calcium-aluminum inclusions, or CAIs.

A balloon in your hand springs back equally in all directions. But a bottle of soda behaves differently: along the neck it is stiff, while across it is easily squeezed. This is roughly how pressure works inside some stars: it can be unequal in different directions. Such stars are called anisotropic, and their behavior has so far been described by disparate methods.

A chemical reaction resembles passing through a turnstile: a crowd creates chaos and gets stuck, while an orderly line moves. In the quantum world, however, when the jostling subsides, the barrier can become ghostly — a particle passes through it as if the turnstile has vanished.

A thrown stone arcs along a clean trajectory, but an electron's position in an atom is smeared out like fog. The transition from one to the other is a puzzle. New work shows that the fuzziness disappears not because of an observer, but because of the particle's own gravity.

Gas falls onto a neutron star — the ultra-dense remnant of an exploded star. This gas accumulates at the magnetic poles and forms a mountain. But a mountain on a neutron star is not like one on Earth: it is held not by rock but by magnetic field lines, like iron filings on a magnet. When there is too much gas, the mountain begins to break apart.

In a disk of gas and dust around a young star, dust particles behave like sand grains in a stream of water: the gas flows faster, the dust lags behind, and friction arises between them. This friction can rock the magnetic waves that run through the disk. The galaxy is full of such disks: it is precisely in them that planets are born.

Drop two identical pebbles from a mountain peak: one lands a centimeter to the left, and a minute later they end up in different valleys. A galaxy is the same mountain, only with billions of pebbles and a slope that stretches over millions of years. The authors of a new study simulated a disk of 40 million point-like stars and tested how quickly it forgets where it started.

In cold clouds of interstellar gas, long, dense filaments stretch out. Inside them, like overcrowded incubators, future stars are maturing. For a long time, it was thought that within such filaments, everything was governed by gravity: matter smoothly flows toward the centers, where density increases and eventually a star ignites.

Around young stars, disks of gas and dust swirl — the building blocks for future planets. Inside these disks, dust grains don't just fly randomly: they align along invisible lines of gas flow. Recently, astronomers noticed that dust grains in such disks behave like badminton shuttlecocks — always turning their long side into the wind.

A powder avalanche isn't just a pile of snow sliding down a mountain. It's a cloud racing downhill at car speed. Inside, snow doesn't lie still: it flies: thousands of tiny particles are caught up in air vortices. Until now, no one had seen what actually happens to each snowflake in this chaos. Now scientists have the first footage.

In the cold gas clouds where giant stars are born, everything is churning with motion. Gas compresses, swirls, and fragments into clumps — the future stars. For a long time, it was thought that the magnetic field brought order here: like invisible threads, it stretched clumps perpendicular to itself. But new observations showed the opposite.

Planets are born from dust. In a disk around a young star, tiny dust grains collide, stick together, and gradually grow like a snowball rolling down a hill. But there's a catch: the gas in the disk moves faster than the dust and drags on it, preventing it from clumping into large chunks. For dust to stick together, there needs to be enough of it.

In a protoplanetary disk, a cloud of gas and dust around a young star, dust grains don't just fly in circles. They are carried by the gas flow, like sand by the wind, and in turn alter that flow. Layers emerge, sliding past each other, and at their boundaries an instability arises — waves and vortices.

A gas cloud the size of a small galaxy is falling into the Milky Way at hundreds of kilometers per second. Such clouds are called high-velocity clouds, and until now no stars had been found in them — only gas. Now, in one of them, named Complex H, astronomers have spotted a pair of young star clusters.

In a constellation where new stars are born, one of them behaves like a faulty lightbulb: sometimes shining steadily, sometimes dimming by a factor of several. Astronomers have been monitoring the star Gaia-GIC-1 for several years and now understand that its blinking is the shadow of a huge dust cloud that periodically passes in front of it.

A galaxy plunges into a dense cluster like a runner into a crowd. The oncoming gas, known as the intracluster medium, strips away its own gas, stretching it into a long, glowing tail. Astronomers call these galaxies jellyfish: they have a body and flowing tentacles of stripped material. But only in a few do new stars ignite within those tentacles.

Glass is a material with attitude. It seems fragile, but powerful invisible forces can live inside it. In chemically strengthened glass, the surface is compressed like a stretched rubber band, while the interior is stretched. When a fast object hits such glass, that rubber band snaps in many places at once. Scientists fired projectiles at glass and watched how it shattered.

A young planet in a gas disk is like a swimmer trying to swim against the current: friction with the gas slows it down, and it spirals toward the star. For small rocky planets, this fall can take less time than they need to grow. But the disk also has countercurrents — vortices that can push the planet outward. Scientists built a computer model of a disk around a young star.

When two tectonic plates grind against each other, a layer of pulverized rock ends up between them, like sand between your palms. This layer, which geologists call fault gouge, behaves not like solid rock but like a thick paste: it can compact, dilate, and slide. Whether a fault ruptures in a devastating earthquake or creeps slowly and safely depends on its whims.

In a tokamak, plasma is like a crowd on a narrow street: once someone starts running, everyone takes off at once. In a stellarator with a non-circular cross-section, the street is winding, with dead ends and pockets. The crowd can't gather into a single wave — people get stuck in different corners.

The Sagittarius galaxy plunged into the disk of the Milky Way and passed through again and again, like a stone thrown into a still pond. Each strike left ripples: waves and warps in the star field.

A giant planet circles too close to its star. With each orbit, it tugs on the star with its gravity, and waves are born deep inside the star, like ripples from a stone dropped into water. These waves damp the planet's orbit, and it spirals into the star. The star swallows the planet and starts spinning faster. Stellar rotation is the key clue.

In the cold clouds of gas and dust where stars will one day ignite, some atoms have lost electrons and become charged. Charged particles feel the magnetic field, while neutral ones do not, so the charged ones slip through the neutral ones like water through a sieve. Astronomers have measured this drift speed: about a hundred meters per second.

A young star is surrounded by a flat, rotating disk of gas and dust — the construction site for future planets. The disk lives its own life: gas flows toward the star, dust clumps together, and from outside, harsh ultraviolet light from neighboring hot stars presses down on it all, like wind blowing leaves off a path.

Around young stars, flat clouds of gas and dust swirl: these are the birthplaces of planets. For matter in such a disk to clump together, it must be constantly stirred. But what makes the gas move chaotically when it would otherwise be calm? Part of the answer lies in the fact that the gas in the disk barely conducts electricity: it is weakly ionized.

Inside giant planets like Jupiter and Saturn, heat doesn't always rise freely. Heavy elements, which are more abundant in some layers than others, prevent hot fluid from floating up. This creates semiconvection — a type of mixing where heat and composition spread at different rates.