gravitational atom

An invisible scaffold holds galaxies together, keeping them from flying apart. This is dark matter — matter that doesn't shine and barely interacts with ordinary stuff. Astrophysicists have long debated what it's made of.

In the far reaches of space, there exists a hypothetical object: an ultracold black hole. It is charged and resides in an expanding universe (de Sitter space). Its temperature hovers just above absolute zero — about one trillionth of a degree above it.

The world around us is three-dimensional, but perhaps that's just an illusion. Some theories allow for extra dimensions of space, curled up or stretched in special ways. One such model depicts a five-dimensional universe with a "diluted" dimension (called a linear dilaton).

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 black hole is like a perfectly dark room: from outside, you can't see what's inside, and anyone crossing the threshold seems to vanish from the outside world. But what does the falling observer feel? In classical physics, nothing special: the event horizon isn't marked by any signpost.

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.

In 1933, Fritz Zwicky first spoke of an invisible mass holding galaxy clusters together. Decades later, Vera Rubin mapped galactic rotation, revealing the ghostly presence of dark matter. Today we know it pervades the cosmos, but its particle nature remains elusive.

The focus is on a black hole, but not an ordinary one. It carries a magnetic monopole and is surrounded by a dilaton — a field that blurs the familiar boundaries of space. The authors tested how stable such a system is to thermal jolts. A magnetic monopole is a hypothetical particle with a single magnetic pole.

The black hole paradox has haunted physicists for decades. If a hole evaporates, where does its contents go? Discoveries by Stephen Hawking and Jacob Bekenstein showed that saving the laws of nature requires an unconventional move. Imagine the universe as a woven blanket of invisible threads.

Two black holes circle in a slow dance, gradually drawing closer. Their motion perturbs spacetime itself, like two heavy balls rolling on a stretched sheet, making it tremble. These tremors are what we call gravitational waves.

A black hole is not just a dark spot in the sky. Its shadow falls on the glowing backdrop of infalling matter and carries the imprint of spacetime geometry itself. If gravity works even slightly differently than we think, the shadow will give it away. In a new study, physicists traced light rays around a rotating black hole in so-called Rastall gravity.

At the center of many galaxies lurks an invisible halo of dark matter: it holds the stars at the edges, keeping them from flying apart. For a long time, it was described as a dilute gas of particles, but new work offers a different view: dark matter might gather into a quantum droplet.

If a black hole spins quickly, it can hold a cloud of ultralight particles around it, so light that their mass almost vanishes. They arrange themselves in layers, like electrons in an atom, only here gravity does the job instead of electric forces. This structure stores energy, like a coiled spring.

The universe is filled with invisible dark matter. Just as a drop of water, as it evaporates, leaves behind a tiny salt crystal, so too can a black hole evaporate, leaving behind a minuscule stable remnant.

In the quantum world, dark matter particles can merge into a single superfluid droplet — a state where matter flows without friction, like an ideal fluid. When near a black hole, this droplet doesn’t just disappear into it but twists into stable vortices, like water swirling around a rock in a stream.

For nearly a century, astronomers have watched galaxies spin as if held together by invisible mass. Fritz Zwicky first noticed it, and Vera Rubin precisely measured the speeds of stars at the edges.

In the standard picture, black holes are the undisputed density champions: all their matter is squeezed into a single point. Imagine the entire mass of Mount Everest packed into a grain of salt. But physicists have found a theoretical trick.

The universe is full of invisible substance that governs the movement of galaxies. In the 1970s, astronomer Vera Rubin showed: without dark matter, stars on the outskirts would have long since flown apart. But what it's made of remains unknown.

A dying star is not just fading away. In its final moments, the core, starved of fuel, collapses into itself at colossal speed. Classical gravity leaves no choice: if the mass is large enough, a black hole is born — a region from which not even light can escape.

In 1965, Penrose unleashed a mathematical thunderbolt on physics: any sufficiently massive star, shrinking under its own weight, inevitably collapses into a singularity — a region where spacetime curvature becomes infinite and the laws of physics break down.

Water boils in a pot, and bubbles rise from the bottom. They grow, float up, and pop, and the water remains water. Something similar, physicists have found, can happen to space itself — if it contains dark energy (the mysterious force accelerating the expansion of the universe). In such an eternally inflating universe, black holes are sometimes born.

The atomic nucleus is not a solid ball but a dense swarm of tiny particles called quarks, glued together by a special glue (the strong force). In light nuclei, such as calcium, this swarm is simply arranged: the numbers of the two quark types, up and down, are almost equal, like the white and black keys in an octave.

After the Big Bang, the Universe resembled a tightly inflated balloon: pressure prevented matter from clumping together. But hypothetical superheavy particles — sort of ‘heavyweights’ of the microcosm — momentarily made the balloon less stiff. Matter easily clumped, giving birth to black holes with masses from a billion to a billion billion tons.

A boiling cauldron with the occasional bubble of steam popping: that's what the early universe resembled. All of space was filled with a field in a false vacuum state, like water superheated above its boiling point.

The Oort Cloud is a spherical swarm of trillions of icy bodies at the very edge of the Solar System, about a light-year from the Sun. These objects are almost motionless relative to one another until some gravitational disturbance breaks their calm.

In the kitchen, there's a bucket of water and an identical bucket of sand. Pour the sand into the water, and you get a mixture where there's exactly five times more sand than water. That's roughly how our universe is arranged: one part ordinary matter — the stuff stars, planets, and we ourselves are made of — and five parts elusive dark matter.

Light reflecting off the scorching disk around a black hole can reveal more about it than we ever thought. When the disk emits heat, some of that light bounces back onto the disk and scatters, acquiring an unusual energy distribution, as if a new component, resembling a power law, is added to the ordinary glow.

When stars at the edges of galaxies rotate faster than calculations based on visible mass predict, standard cosmology invokes the hypothesis of hidden dark matter — invisible substance that reveals itself only through gravity. A new study offers an alternative that requires no new particles.

When two black holes collide, they send out gravitational waves and ring like a massive bell. The fading sound, or ringdown, carries the imprint of the final black hole. But if dark energy, the force accelerating the universe, changes over time, it can cling to the black hole like a thin paint layer.

An atom excited by light gives its energy back in an instant — it emits a photon. This process is like a tired runner dropping a heavy load. But if the runner is on a mountain slope, it's harder to pick up speed. Gravity acts on the atom similarly: near a massive body, time flows slower, and the atom emits differently.

Black holes are rarely alone in the cosmos. They are often shrouded in invisible clouds of hypothetical dark matter particles — so light that they feel only gravity, barely interacting with each other or ordinary matter.

When liquid is swirled in a cup, a vortex with an empty center forms. In this empty core, waves find a trap: bouncing off the walls, they siphon energy from the vortex and grow like a flame along a fuse — each wave stronger than the last, until a surge breaks loose. Astrophysicists have described the same chain reaction around black holes.

Typically, a black hole is a region from which nothing returns. But an exact solution to Einstein's equations, combining a solitary Schwarzschild hole with the Lemaître expansion of the universe, paints a different picture.