massless scalar field

A black hole spun up almost to its limit is like an athlete balancing on the edge of a record. The most interesting action isn't inside the hole itself, but in the thinnest film of spacetime at its horizon. It's there that tiny corrections to Einstein's gravity can suddenly swell to gigantic proportions.

A classical black hole is a bottomless well: everything that falls past the horizon disappears into a point of infinite density. But in loop quantum gravity (one approach to quantum gravity), that point is replaced by a quantum 'bounce'—a sphere of finite size where spacetime doesn't tear but rearranges itself.

Light from afar bends around a black hole like a cyclist taking a sharp turn. Get closer, and it starts looping around an invisible sphere of photons. Every black hole has such a sphere, but usually it's wobbly: the slightest nudge sends light flying away or falling in.

A black hole is a gargantuan cosmic whirlpool that drags in everything nearby. But beyond visible matter, an invisible mist can hover in its vicinity — dark matter. Physicists have studied its behavior. Unlike ordinary matter, the field doesn’t necessarily fall through the horizon.

$$10^{-35}$$ seconds. A tiny instant during which the Universe manages to expand by a factor of $$10^{26}$$. Immediately after, it goes through thousands of rapid transformations — like a ball bouncing along a chain of tunnels. This cascade is the essence of chain inflation, first proposed by Alan Guth.

A cloud of waves collapses under its own gravity. While it's loose, everything goes by the book: the field oscillates gently in nearly flat space, and approximate formulas work perfectly. But add just a bit more energy, and the picture changes. Physicists used a numerical model to catch the moment when simple calculations stop describing reality.

At the center of a galaxy sits a supermassive black hole, surrounded by a vast, tenuous cloud of dark matter. It doesn't shine or heat, but its gravity warps space and changes the rules of the game for everything orbiting nearby.

Gravity is the invisible glue that holds stars and planets together. But what if this glue has a tiny mass? In massive gravity, the carrier particles (called gravitons) weigh a minuscule but nonzero amount. This changes the rules near black holes. The authors of the new study built on a mathematical tool — eigenvalue decomposition.

The death of a massive star is not just the flash of a supernova, but also the birth of a black hole.

At the center of attention is a black hole of unusual shape. Its geometry resembles a spindle: a slight elongation is added to the usual rotation. The parameter B measures this deformation. The spindle deformation is not just a mathematical toy.

The quantum world is often compared to a musical instrument. Each system, whether an atom or a chain of particles, sounds at its own frequencies, which physicists call energy levels. In chaotic systems, like an orchestra without a conductor, these frequencies usually fill the entire available range without gaps.

In classical theory, a black hole is where matter collapses to a point of infinite density. Such a 'singularity' looks like an error in the equations: nature hardly tolerates infinities. Many physicists seek ways to 'smooth out' this flaw, and one idea is to modify the theory of gravity itself at small distances.

At the center of an ordinary black hole, according to classical ideas, lurks a singularity — a point of infinite density where the laws of physics break down. But some theories, inspired by the duality idea from string theory, propose replacing the point with a tiny 'smudged' region.

A black hole's interior is layered like an onion. In the new model, instead of an infinite point at the center, there are three regions: a dense core, a transition layer, and a crust just below the horizon. All arise from a single field that interacts with itself.

A textbook black hole resembles a perfectly smooth sphere: everything outside it calmly flies off to infinity. However, quantum gravity paints a different picture. Recently, within loop quantum gravity, a solution was found — a 'Kruskal' black hole where spacetime beyond the horizon behaves differently.

Space is threaded with magnetic fields. They exist around galaxies, stars, and even in nearly empty voids — the vast empty spaces between galaxy clusters. It's usually thought that fields are amplified from weak 'seed' fields by turbulence, much like a dynamo. But the origin of the seed fields themselves has remained a puzzle.

A black hole with a magnetic field resembles a whirlpool in a river, where water doesn't flow into the vortex but swirls in place. Usually, the hole's rotation picks up waves and amplifies them: this is called superradiance. But add a magnetic field, and everything changes.

A tiny star spirals around a giant rotating black hole. Slowly, it moves closer in a spiral, and this dance lasts thousands of years. All the while, waves ripple through space, like ripples on water, but these are gravitational waves. They can be "heard" with special detectors.

Spacetime is not empty: it shivers. After the Big Bang, the universe was filled with a hum of gravitational waves, like the low rumble of a giant bell. In this ripple, as it turns out, particles of dark matter, the invisible substance that holds galaxies together, can be born. But the previous idea had a snag.

In the microscopic world of the strong interaction, nature's most powerful glue, quarks never wander alone. Over large distances, they stick together into the protons and neutrons we know. But under extreme compression, like in the depths of a neutron star, this glue creates far more exotic forms of matter.

At the center of a galaxy, a huge black hole is shrouded in an invisible cloud — a swarm of ultralight particles that it itself spawned. Into this cloud dives another black hole, about the size of a star, and begins a long spiral dance. The approach takes millions of years, but the most dramatic events unfold right at the horizon.

Two magnets collide in a dark room, stick together into a clump, and a dull thud echoes. Black holes behave much the same way, except instead of magnets they carry electric charge, and instead of a thud, there's a burst of gravitational waves. But there's a third player in this story — an invisible field that physicists call scalar.

A billiard game would be strange if the balls had no mass. They wouldn't collide but would pass through each other, ignoring obstacles. That's roughly what it looks like to imagine light as a stream of classical particles — tiny elastic bodies flying in straight lines. A new proof puts an end to that picture.

A wormhole is like a tunnel with a very narrow throat. If you send a sound signal into such a tunnel, part of the echo returns, while part gets stuck in the middle, and will leak out very slowly.

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.

Emptiness can surprise you. In general relativity, there is a solution where space itself gives birth to a black hole — literally from a point. It all starts at the moment when the event horizon (the surface from which not even light can escape) appears with zero radius and immediately begins to grow.

The oldest light in the universe has been traveling toward us for nearly 14 billion years. It was born when the cosmos first became transparent, and since then its plane of oscillation has been rotating ever so slightly. The cause is an invisible ocean permeating all of space: the dark energy field that makes the universe expand faster and faster.

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.

In the usual picture, a black hole is a featureless pit in spacetime. But if a shell of matter vibrates around it, the gap between the edge of the abyss and this shell becomes a resonant cavity.

Drop a handful of sand into calm water — the ripples spread and fade. Drop it into a running blender — the vortices mix everything in an instant. Physics has a similar rule: chaos cannot grow faster than a certain rate.

A fluffy ball of invisible web envelops a black hole. This web is dark matter, which doesn't shine but, through its weight, governs the motion of stars on the outskirts of galaxies. Astrophysicists have long seen such 'fluffy' clouds around cosmic objects and have mapped their profiles — how density falls from the center to the edge.

Ordinary matter, described by the Standard Model, is stars, planets, light. But it makes up only a tiny fraction of the cosmos. The rest is dark matter, born after the Big Bang. What's it made of? Possibly ultralight particles. New work shows how two types of such particles can amplify ordinary light.

Usually, a black hole is an abyss with a point-like dip at the center, where density is infinite and everything breaks down. Einstein and Schwarzschild described such a scenario. But infinity is a sign that the theory stumbled.

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.

Einstein and Rosen imagined a bridge connecting two sheets of reality. Wheeler gave it a name — wormhole, and Thorne with Morris proved: the tunnel is traversable if you fill it with exotic matter.

Hold a magnet near a pile of iron filings, and they line up along invisible lines — the field wraps around the magnet from pole to pole. In a similar way, you can visualize gravity around massive bodies: instead of filings, it's space itself; instead of a magnet, a star or a black hole. The authors propose decomposing gravity into two fields.

Spacetime sometimes resembles a sheet of paper in which you can punch a hole and connect the edges with a short tube: you get a wormhole. In the simplest mathematical models of such wormholes, massless scalar fields appear — something like an invisible fog filling everything around.

A swing swings higher and higher if you push it in rhythm. A similar mechanism kicks in when a dead star orbits a massive black hole shrouded in a cloud of ultralight particles. These particles are candidates for dark matter — the invisible substance that keeps galaxies from flying apart.

A magnetic field can hold a star against complete collapse: that's the idea behind a new kind of black hole. Instead of the usual point of infinite density, inside there is a field that prevents space from crunching down to zero. It's like a spring: the harder you squeeze, the more it pushes back.

A top spun to its limit changes the air flow around it — the air swirls differently than around a barely spinning top. Black holes in some extended theories of gravity behave similarly. When a hole spins fast enough, the curved spacetime near its poles acquires new properties.