mass transfer

A neutron star is the remnant of an exploded star, compressed so tightly that a teaspoon of its material would weigh as much as a mountain. Inside such an object, protons and neutrons are packed tightly together, and under enormous pressure, hyperons, particles containing a strange quark, can appear.

Two stars circle each other like dancers who come together and drift apart. Over time, one swells, and its outer layers spill onto its neighbor. The star that receives foreign matter looks no different from a single star, but its surface remembers everything.

A balloon that lets out air in bursts zips around the room — the jet blasts first one way, then another. A dying star behaves the same way as it sheds its bloated shell. Only instead of air, it's superheated gas, and instead of a balloon, it's a future white dwarf (the dense stellar remnant about the size of Earth).

Around a just-ignited star swirls a vortex of dust and gas. This vortex, the protoplanetary disk, grows by accreting material from the surrounding cloud.

Deep inside molecular clouds hide natural amplifiers — cosmic masers. They work like lasers but in the radio band: excited molecules collectively emit waves of a single frequency, creating a bright beam. The catch is that these molecules often have several ways to shed energy.

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.

It takes the stellar pair J05+50 nearly two months to complete one orbit around their common center. From Earth, it appears as a faint point in the constellation Hercules — 4625 parsecs away. Photometry of the binary star only captures a steady flicker of brightness, like the pulse of a giant heart.

Two figure skaters on a lake frozen to the horizon. They are so far apart that their silhouettes turn into dots, and their mutual attraction becomes almost an article of faith. By Newton's law, they should circle in an unimaginably slow waltz. But telescopes see otherwise.

A quarter-century ago, Michel Mayor and Didier Queloz discovered the first hot Jupiter, and shattered all the rules of planet formation. A gas giant on a days-long orbit couldn't have formed next to the star: it's far too hot and lacks building material. So, it must have been born far away and then migrated.

At the center of the Milky Way, where the supermassive black hole Sagittarius A* reigns supreme (its metric first derived by Karl Schwarzschild), star S4714 makes a dizzying voyage.

A planet the size of Neptune wandered too close to its star. The star begins to pull the planet's outer layers onto itself — gas streams off the planet like water from an overflowing bucket. This process is called Roche-lobe overflow (astronomers use this term for the boundary beyond which a star can tear material away from a planet).

Two stones fall into a pond. Ripples spread from each, but when they collide, there's a splash and a short, sharp clap. That's roughly what the merger of two neutron stars sounds like: those ultra-dense remnants of exploded stars.

Picture a tightrope walker balancing over an abyss. Every step changes the rope's tension, and the slightest shift in center of gravity can prove fatal. That's roughly what the dance of an ordinary sun-like star around a black hole of ten solar masses looks like when the orbit is highly elongated.

Detectors pick up the “ripples” of gravitational waves from mergers of black holes or neutron stars — like an echo from the kitchen where a cosmic dish was being prepared. Astronomers are trying to reconstruct the recipe: how two massive stars turned into an exotic pair and collided.

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.

In space, merging black hole pairs are common, and often one is noticeably more massive than the other. This mass difference isn't just a number: it's a key to their shared history. Astrophysicists studied the stable mass transfer channel — a process where matter flows smoothly from one star to another without disrupting the system.

A lighthouse blinks steadily once per second. If it moves in a circle, its flashes arrive sometimes a bit early, sometimes a bit late, and they give away an invisible companion. That's exactly how astronomers exposed the hidden partner of the star IY Lyrae. IY Lyrae is a pulsating variable star in the thick disk of the Galaxy.

Two black holes, orbiting each other, behave like a boat rowing with stars. Each passing star is flung away, like a stroke of an oar, and transfers momentum to the pair. For a long time, it was thought this simply brings the black holes closer. But new analysis has shown: by flinging stars unevenly, the system pushes itself sideways, spins, and tilts the orbit.

The latest crop of gravitational waves brought a puzzle. The LIGO, Virgo, and KAGRA detectors caught dozens of signals from merging black holes, and the mass plot shows a glaring gap: objects heavier than 45 Suns are almost absent, and the few that exist spin suspiciously fast. Some say giant stars explode too 'cleanly,' leaving nothing behind.

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.

Two stars orbit a common center, accreting gas from a surrounding cloud. Rotating disks of gas form around each star and around the pair as a whole. From these disks, jets shoot out like hoses. Inside the disks, gas is constantly churned — that's the magnetorotational instability at work.

Young planetary systems resemble an orchestra that has just started rehearsing: all the musicians strive to play in the same rhythm.

Two faint embers circle each other in the dark so closely that one begins to tear glowing chunks off the other. That is the picture of the system ZTF J1239+8347, caught by the Zwicky Transient Facility telescope.

A sugar cube sits on a saucer next to a cup of hot tea. Drop it in, and it dissolves within minutes. But if you lower it slowly, the sugar melts gradually, releasing its sweetness into the drink. Something similar is happening in two newly discovered stellar pairs, except the sugar is a brown dwarf and the tea is a star.

Two dim stars whirl so close together that one siphons material off the other, like a spoon delicately skimming foam from broth. Astronomers have for the first time calculated the fate of such pairs — ultracool and brown dwarfs, the coldest and dimmest inhabitants of the galaxy. Previously, it was thought that mass exchange between them was impossible: they were too fragile.

On a deserted road at night, a streetlight flickers rarely but at full power. That's how WZ Sge-type stars behave: they smolder barely noticeably for years, then suddenly flare hundreds of times brighter. Astronomers decided to check what happens in their gas disks during quiescence, and found almost emptiness.

In the star cluster NGC 2158, which is over a billion years old, astronomers have counted how often stars live in pairs. The Hubble telescope stared at the cluster for a long time to catch even the faintest stars: those lighter than one-third of the Sun.

For 39 years, astronomers have been recording how the star BE Lyn brightens and dims. Its light pulsates with a rhythm of several hours, like a lighthouse that never stops blinking. But there is a glitch in this rhythm: sometimes the flashes came a little early, sometimes a little late. The star was moving closer to Earth and then farther away, as if something were dragging it in a circle.

In a star cluster, like on a crowded dance floor, massive stars rarely stay single. More often they whirl in pairs or triples, and the distance between them can be less than from Earth to the Sun. But how do they manage to get so close to each other? Simulations showed: it's all about the disk of gas and dust that envelops the pair. This disk, like a drain funnel, swirls the stars and slowly pulls them inward.

The young binary star IRS 44 in the constellation Ophiuchus resembles a bustling kitchen: streams of gas, like jets of dough, fall onto a rotating disk, and where they strike, heat is born.

Two stars whirl in a tight dance. One is a neutron star — an ultra-dense sphere the size of a city but with a mass of one and a half Suns. The other is an ordinary star that swells and spills its matter onto its neighbor. Sometimes this transfer happens too fast, and the stars become enveloped in a shared gas shell, like two spoons in one pot of boiling soup.

Short gamma-ray bursts are colossal explosions that release, in a fraction of a second, energy comparable to what our Sun will emit over billions of years.