structure growth

An old stellar ball that has gathered hundreds of thousands of suns has been circling the edge of a dwarf galaxy for billions of years. By all calculations, it should have long ago plunged into the center like a heavy stone into jelly. But the ball holds its ground, and this fact has been nagging astrophysicists for several decades.

A census by body shape: that's one way to describe what astronomers did with 6348 massive galaxies. Instead of height and weight, they measured how concentrated the light is toward the center, how flattened the galaxy is, and how asymmetric its shape is. Then they ran the same measurements on galaxies from three computer models of the universe and compared the results.

In the dark room of the scanner, a person watches for rare flashes on a screen. An infrared camera records their pupil a thousand times per second, while an MRI scanner simultaneously logs which brain areas light up. In this way, 89 volunteers aged 19 to 78 helped scientists see how the pupil becomes a display on which the brain outputs two different signals.

An old city gains new suburbs. In the center, narrow streets where life has nearly stopped, while on the outskirts construction is booming. That is what a spiral galaxy looks like when its core stars have long aged and new stars are still being born in the outer disk.

Imagine a factory capable of producing a million parts per hour, yet it only makes a hundred. That's roughly how our Universe behaves when viewed through the lens of entropy — a measure of disorder that, according to physics, must only increase. The main "machines" of this factory are supermassive black holes.

A jazz ensemble: at first, a cacophony of random notes. Then — a catchy riff that plays over and over. Such is the riddle of the origin of life — only in the language of chemistry.

The standard cosmological model ΛCDM (which includes dark energy and cold dark matter) is the score of a cosmic symphony. It describes how space expanded after the big bang. How dark matter clumped together. How galaxies ignited. For a long time, everything played flawlessly.

In 1929, Edwin Hubble pointed his telescope at distant galaxies and discovered they were receding. Ninety years later, two measurements of this recession rate, from ancient light and from nearby stars, stubbornly disagree. A 9% discrepancy cannot be chalked up to error. It is as if the Universe in its youth and in its maturity runs on different clocks.

The universe is like a vast invisible scaffold. We don't see it directly, but we know it's there: galaxies and clusters hold together thanks to it. This scaffold is dark matter. The most popular version says it is "cold," made of heavy, slow-moving particles.

The cosmos resembles silk fabric with threads of the dark web showing through. We only glimpse tiny swatches of the real tapestry — through telescopes, in actual galaxy catalogs. To separate the fundamental signal from astrophysical noise in the cosmic pattern, statistical analysis demands thousands of plausible sketches — synthetic sky maps.

Picture the early Universe as an unimaginably large bell. Inflation — the era of rapid expansion, dreamed up by Alan Guth, strikes it, sending a wave rippling across the fabric of spacetime.

Ever since Fritz Zwicky noticed that galaxy clusters were moving too fast, and Vera Rubin measured the rotation of spiral arms, dark matter has remained cosmology's greatest mystery.

When the cooling cosmos, in the aftermath of the Big Bang, lost its primordial symmetry, tensions arose in the fields, like microcracks forming in solidifying glass. Global monopoles, predicted by Gerard 't Hooft and Polyakov, became such “scars” on the fabric of the universe. Each monopole is a tiny but incredibly massive knot of field.

When we peer deep into space, we see the past. Edwin Hubble’s law turns redshift into a time machine: light from galaxy UDS 12999 traveled to us for 7.6 billion years — more than half the age of the Universe.

In the first moments after the Big Bang, the Universe was not a silent void but a seething cauldron of plasma, threaded with sound waves. As the temperature dropped, the cosmos underwent phase transitions — spontaneous reorganizations that gave birth to bubbles of a new phase.

In the search for the nature of dark matter, one of the most intriguing hypotheses traces back to the first moments after the Big Bang. Back then, quantum fluctuations of the inflation field gave rise to clumps of matter that could collapse into primordial black holes.

The story began with a missing mass. In the 1930s, Fritz Zwicky, measuring velocities in galaxy clusters, first suspected the presence of invisible matter. Later, Vera Rubin showed that the outskirts of spiral galaxies rotate too fast for the visible matter.

The hot broth of the early universe cooled unevenly. At some point, bubbles of a new phase began to pop within it, like steam bubbles in boiling water. But these bubbles weren't made of steam; they were made of a new state of matter in which particles of the dark sector clumped into larger lumps. That's how dark matter could have been born.

At the center of a galaxy, gravity condenses dark matter into a dense 'spike.' Such a dark spike resembles a funnel of invisible particles around a massive body. But if both the center and the particles are primordial black holes, the picture breaks down.

Lenticular galaxies are the cosmic quiet types: they have a disk but no bright spiral arms. For a long time, their origin remained a mystery. A team of scientists ran the Hydrangea computer simulation and traced the fate of each galaxy from its youth to the present day. On the mass–size diagram, these galaxies line up in a V shape.

The Universe grows like a metropolis: galaxies skyscrapers are erected on an invisible scaffold of dark matter: its gravity pulling in construction material. Meanwhile, dark energy makes the city itself continuously expand.

Putting together the Solar System is like crafting a high-end tasting menu: the recipe isn't always set in stone — sometimes the final ingredient is added while the dish is already cooking.

Using the James Webb telescope, astronomers peered into an ancient quasar — the dazzling heart of a galaxy where a giant black hole sucks in matter. It turns out it doesn't just destroy, but also creates: its powerful outflows and shock waves act like a true cosmic mill.

Through the ripples on the water, pebbles at the bottom of a pool look shifted and warped. In a similar way, the gravity of invisible dark matter bends the light of distant galaxies — a phenomenon known as weak lensing.

A blacksmith forges a sword. With each hammer blow, the red-hot metal flattens, but the hammer, the anvil, and the surrounding air all warm up slightly. Part of the impact energy is irreversibly lost as heat — a trade-off familiar to anyone who has ever driven a nail, and it turns out to be the key to the biggest mysteries of the cosmos.

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.

A balloon doesn't deflate all at once: first, dents appear on its surface, which run, merge, and finally the balloon shrivels into a point. Domain walls behave in much the same way — thin partitions that divided space in the first moments after the Big Bang.

In a city park, trees grow faster than in a deep forest — not because the soil is better, but because branches collide and seeds are exchanged more often. Galaxies in the Spiderweb protocluster behave much the same way. This vast clump of matter will become a mature cluster billions of years from now.

In the seething cauldron of the early universe, the vacuum, like a supercooled liquid, could boil with bubbles of a new phase. For a long time, physicists pinned their hopes on these bubbles as a source of primordial black holes (PBHs)—ideal candidates for dark matter.

If you don’t stir a layered cocktail, the heavy syrup sinks to the bottom. A young planet is much the same — a seething ocean of molten rock. As it cools, minerals crystallize: some, like iron, get heavy and sink, while others float. You’d think a dense layer would pile up at the core.

A crowd in a city square behaves differently depending on whether people hold hands. If each person only lightly touches a neighbor's elbow, people easily spread out in all directions — the crowd expands as a smooth carpet. But if they interlock fingers, movement slows down and the crowd breaks into clumps: dense clusters form here and there, with empty corridors between them.

Giant galaxy clusters are cities of thousands of star islands, held together by gravity. Inside them, hot gas churns and glows in X-rays. If a cluster has recently collided with another, it develops clumps of galaxies and distortions in the gas, like ripples on water after a stone is thrown.

Globular clusters are dense 'balls' of hundreds of thousands of stars that orbit the center of the Milky Way. Some were born in our Galaxy, others were captured when the Milky Way swallowed dwarf satellite galaxies. They can be distinguished by chemical composition, but astronomers now have a new tool — dynamical age.

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.

A balloon inflates on its own, even though no one is blowing it up. That's roughly how the accelerated expansion of the universe looks, and to explain it, scientists usually invoke dark energy, an invisible and poorly understood force. But what if the balloon expands because new air molecules are continuously appearing inside it?

Every shell is a stone diary of growth. The mollusk doesn't build it from a blueprint like an architect; it simply adds material along the edge, following the same rule over and over. It's as if a snail glued a new strip to its house each day, nudging it slightly sideways and making it a bit bigger. It's this repetition, not complex control, that creates the species' characteristic shape.

A tiny black hole the size of an atomic nucleus floats in the hot soup of the early universe. Normally, such a little one should quickly evaporate, releasing energy like a drop of water on a hot skillet. But if space is more complex than it seems and contains hidden dimensions, everything changes.

No one has ever seen dark matter, but every galaxy feels its pull. Usually, it's pictured as a sea of identical, silent particles. The new work paints a livelier picture: two kinds of particles, heavy and light, constantly exchanging between them.

In a cloud, thousands of tiny water droplets hang in the air. For rain to fall, they need to grow: stick together into larger drops and become heavy enough to fall to the ground. But how exactly do droplets find each other in a huge cloud? Scientists created a computer model that tracks each droplet individually, as if each one had its own little sensor.

Two galaxy clusters collided like two swarms of bees flying through each other. One of them is the famous "Bullet." After the collision, the hot gas, which makes up most of the ordinary matter, slowed down and stayed in the center, while the galaxies, like small dense pebbles, flew on.