mass ratio

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.

At the center of a galaxy, where a supermassive black hole spins a disk of scorching gas around itself, giant stars sometimes form. They are unlike ordinary stars: the disk continuously feeds them with matter, and a star can grow to hundreds of solar masses, staying bright as long as the gas flow lasts.

A black hole is like a spinning top that never stops on its own. But if a cloud of ultra-light particles, bosons, forms around it, the picture changes. This "fog" acts like an invisible brake: the particles drain the hole's spin, slowing it down.

A white dwarf is the former core of a star like the Sun, squeezed down to the size of Earth. A teaspoon of its material would weigh several tons. A neutron star is an even denser remnant: a city the size of Manhattan, but with more mass than the Sun.

A rotating black hole is no calm whirlpool. Space around it shudders and rings at the slightest disturbance, like a guitar string after a pluck. These oscillations are described by the Teukolsky equation — a complex mathematical construct that physicists have studied for half a century. Recently, a strange symmetry was noticed in this equation.

Two black holes circle in a cosmic dance, spiraling closer together. In the end, they merge into one, and that moment unleashes a powerful burst of gravitational waves, ripples in spacetime itself. But what remains after the merger?

A galaxy collision is like a slow dance in which two partners gradually draw closer. Hidden at the center of each is a supermassive black hole — an invisible flywheel with a mass of millions or billions of suns.

In the galaxy NGC 1052 DF2, stars move at only 8 kilometers per second, as if there were no invisible mass around. For comparison: in our Milky Way, outlying stars accelerate to 200 kilometers per second, held by a massive dark matter halo.

Layer by layer, artifact by artifact — an archaeologist reconstructs the history of an ancient settlement. Similarly, astrophysicists sifting through 259 records from LIGO–Virgo–KAGRA saw a clear layered structure among merging black holes.

The fastest wind in the Universe travels at 0,58 times the speed of light. It covers the distance from Earth to the Moon in two seconds. This wind is not a jet stream but a broad flow of gas erupting from the center of a galaxy. Not all black holes work the same: some create such hurricanes, while others produce narrow plasma beams.

On November 23, 2023, LIGO detectors caught something strange. The gravitational wave signal from a black hole merger, designated GW231123, pointed to record masses—137 and 101 solar masses, and anomalously fast spin. That would be the most massive and fastest-spinning pair ever detected.

Three milliseconds before the merger. A gargantuan black hole spinning at breakneck speed drags in a neutron star — a ball the size of a city but with 1.5 times the Sun's mass. Tidal forces stretch the star into a thread as thin as a needle and fling its matter outward.

In a single star system, two teams of planets orbit. Some follow neat paths, like figure skaters on an ice rink, avoiding collisions. Others crowd together, their trajectories cross, and sooner or later a cosmic accident occurs — a giant impact.

In August 2019, the LIGO and Virgo detectors picked up gravitational waves from the merger of two compact objects in a binary star. One weighed 23 solar masses — a standard black hole. The other came in at 2.5–2.67 M⊙.

In 2017, the LIGO and Virgo detectors recorded the spacetime tremor from the collision of two neutron star merger — event GW170817. After the initial burst came an after-ring: a kilohertz oscillation of the newly formed superdense remnant.

In May 2020, the LIGO and Virgo detectors picked up a gravitational-wave burst known as GW200105. Among the many similar gravitational waves recorded, this one stood out for an oddity: the orbit of the colliding neutron star and black hole was not a perfect circle, but a stretched ellipse.

Two ultradense spheres, each the size of a city, whirl in a dance. Their masses are less than the Sun's, but inside them is matter compressed to unimaginable limits. One sphere is a neutron star; the other is a strange star, made entirely of quarks — the elementary particles that build up protons and neutrons.

The universe rewrites its history again and again. Where ordinary astronomy sees only a point, a black hole, gravitational waves peel back thin layers of the past, like an ancient palimpsest. The idea that black holes can grow by devouring each other, and their offspring can enter new unions, has been discussed by astrophysicists for half a century.

In the heart of a dense star cluster, a true forge reigns: here stars, like glowing blanks, collide and merge under gravity, and these mergers are not a catastrophe but an opportunity. Each strike of the stellar hammer transfers spin to the future black hole.

Traditionally a black hole was described by three parameters — mass, charge, and angular momentum.

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?

The cosmos sets its own lenses in the path of gravitational waves. When two black holes merge, the resulting ripple travels through the universe. If it encounters a massive galaxy cluster along the way, its gravity bends the path of the waves — much like glass focuses light.

At the center of galaxy M87, 55 million light-years away, lurks a black hole with a mass of 6.5 billion Suns. In 2019, the Event Horizon Telescope (EHT) gave us its first portrait: an orange donut with a dark core. But the donut is not the abyss itself.

Think of a merry-go-round: it's easier to spin a light one, harder to spin a heavy one. Neutron stars, the ultra-dense remnants of exploded stars, behave in a similar way. Astronomers looked at fifty binary systems where one neutron star orbits another and noticed: the heavier the star, the longer its spin period. The link isn't strict, but it's statistically noticeable.

A figure skater spins on the ice, gradually spiraling inward. Similarly, a small star or black hole orbiting a massive black hole loses energy. It emits gravitational waves — ripples in spacetime that detectors on Earth pick up. But the dance of this pair is more intricate than it seems. The small companion isn't just a point.

Gravitational-wave detectors picked up a strange burst — the signal GW241011. Two black holes merged, but the pair looked unusual: one hole was about three times lighter than the other, and the system as a whole was spinning rapidly. Such a combination is a rare guest in the catalogs.

In the boundless night of space, galaxies come together in a slow gravitational dance, merging into one. Such collisions are not head-on impacts but rather like fingers moving slowly through water, leaving swirls and tails behind.

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.

Two heavy spheres of dark emptiness hurtle toward each other and collide dead-on. This is not billiards: it's the collision of two equal black holes. The impact sends a tremor through space itself — gravitational waves. Most of this tremor is a low hum that physicists call bremsstrahlung.

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.

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.

Light passing by a black hole swirls like water down a bathtub drain. The most intriguing part is the thin ring where rays can orbit forever, neither falling in nor escaping. This is the photon sphere — an invisible boundary that paints the hole's shadow on the sky.

Drop a stone into a pond, and ripples spread outward. Something similar happens inside compact clumps of dark matter when they encounter a special medium — a scalar field. This field, which pervades everything around us, can spontaneously intensify in the depths of such objects, much like ripples on water growing ever taller and more pronounced.

Pairs of black holes dance in three different styles before merging. The first is a neat waltz: the objects swirl in the same direction, like partners facing the same way. Such pairs are born from binary stars and often have unequal masses. The second is chaotic disco: spins are scattered, masses nearly equal.

In 2017, detectors picked up a tremor in space — gravitational waves from the merger of two neutron stars. Telescopes immediately found a flash of light: a cosmic explosion astronomers dubbed a kilonova. In that fiery cauldron, it turned out, the heaviest elements of the periodic table are born — gold, platinum, uranium.

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.

For a long time, a void yawned in the family of ultra-dense remnants of dead stars. Neutron stars, swift city-sized tops, rarely weigh more than two Suns. Black holes start at about five solar masses. Between them lies a 'gap' where for decades no object could be found.

The event horizon of a black hole is often depicted as a one-way membrane: everything falls in, nothing comes out. But what if it's not an empty boundary but a cloud of the tiniest 'bits' of spacetime itself?

Two black holes fly toward each other and collide head-on. In the familiar picture, their horizons (the surfaces from which not even light can escape) stretch toward each other like water droplets and merge into one smooth shape. But calculations show otherwise: before merging, a sharp beak, a cusp, extends from each horizon.