dark ages

In the first half-billion years after the Big Bang, galaxies grew like crazy. Gas fell in rapidly and collapsed into stars without any resistance. This period is called 'unimpeded star formation.' It's like frying pancakes on a scorching skillet without a lid: splatters fly, but nothing holds them back.

In the KH 15D system, two young stars orbit a common center, and between them and us lies a huge dust disk, like a curtain that sometimes hides the stars and sometimes reveals them. For seventy-five years, astronomers have watched this "theater of shadows": sometimes the light nearly went out, sometimes it flared up with renewed vigor.

When stars are born in a galaxy, they make hydrogen glow, like a neon sign, but on a cosmic scale. This light could tell us a lot about how many stars are forming, but on its way to us, it passes through cosmic dust. Dust is like a fogged-up window: it dims the glow and alters its color.

The JWST spectrograph caught a barely perceptible dip in the spectrum of a distant galaxy — two lines, like shadows cast by cold gas. These are the sodium lines, the very yellow light of streetlamps. Here, at the edge of the visible Universe, they betray the slow exhalation of a galaxy returning matter to space.

Boiling water in a pot is a good place to start. Bubbles of steam rise, pop, and the surface settles down. Something similar might have happened in the first moments of the universe's life with a special field filling space: bubbles of a new phase inflated and collided, like islands of steam in liquid.

For a long time, cosmology was dominated by the belief, originating from Hawking: during the radiation era, primordial black holes do not grow.

The standard cosmological model ΛCDM, where dark matter and dark energy act as the chief architects of the cosmos, has predicted astronomical data with Swiss-watch precision for decades. Its foundation was laid by three geniuses.

Dark matter remains one of the greatest mysteries of modern physics. Back when Vera Rubin observed galaxy rotation, she proved that visible matter is insufficient to keep stars from flying apart.

In the first moments after the Big Bang, the universe inflated at an unimaginable rate. This inflation left behind ripples — tiny overdensities in the hot radiation and plasma.

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.

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.

It all began not with emptiness, but with a boiling ocean of plasma. In that primordial broth, sound waves raced through the fiery matter, colliding and compressing it. Sometimes a clump grew so dense that light could no longer escape, and right out of the scorching gas, a primordial black hole was born.

The early universe underwent a rapid expansion — inflation. In a tiny fraction of a second, minuscule quantum jitters were stretched to galactic scales and became the seeds of all large-scale structure.

A bonfire doesn't burn out all at once. If you glance at the flames at a random moment, all you see is a jumble of fire tongues, and you can never tell what exactly burned: a wet branch, an old magazine, or an armful of dry grass. But if you watch the fire hour after hour, rhythms emerge in its dance: a burst of heat, a lull, a change in color. These rhythms tell the story of what was thrown into the flames.

Civilizations in the Universe are separated not just by distance, but by the vast gulf of time. Hunting for their traces is like archaeology: instead of palace ruins, we find clouds of cosmic dust.

The origin of the hot Big Bang is one of the greatest mysteries. The familiar picture: after inflation, the inflaton field transfers energy to ordinary particles, reheating the Universe. Yet dark matter and dark energy hint that nature has hidden sectors.

A sponge thrown into a bucket of water eagerly soaks up moisture and swells before your eyes. But if you keep adding water and squeeze and release the sponge, absorption becomes harder and takes longer. That's roughly how tiny black holes behaved at the very beginning of the universe.

Our Solar System isn't an island in the void: it's a sensitive web stretched in a dark cosmic corner. Planets circle their orbits like dewdrops on threads, and we are the spider sensing the faintest tremor. That tremor betrays the approach of the catastrophe astronomers call the Big Rip.

The JWST telescope has spotted a multitude of bright galaxies in the young universe. Their ultraviolet light was barely absorbed by cosmic dust — defying previous expectations.

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.

There is something wildly generous about a garden where the first flowers don't just bloom but immediately scatter their seeds far beyond the fence. Something similar was happening in the young universe.

In a vast dark hall, someone invisible plucks the strings. The cosmic gas, the tenuous hydrogen that filled the young universe, resembles stretched strings that can resonate at a radio wavelength of 21 centimeters. This is hydrogen whispering about its temperature.

In the first moments after the Big Bang, the cosmos resembled a giant cooling pond. Just as water, when freezing, becomes covered with a network of cracks, so the cooling universe could have cracked — not into ice, but into the thinnest filaments of pure energy. These filaments are called cosmic strings.

After the Big Bang, the Universe was filled with cold gas — mostly neutral hydrogen and helium. It enveloped the cosmos like a morning fog, impenetrable to light. The Dark Ages began. When the first galaxies ignited, their radiation, like a searchlight beam, started knocking electrons out of atoms.

The density at the center of a neutron star is so extreme that a teaspoon of its material would weigh as much as a mountain. Physicists have long tried to figure out how massive such a star can get before it collapses into a black hole.

In 2015, astronomers were examining the Coma galaxy cluster and noticed something odd: huge, almost invisible "fluff balls." These galaxies are as large as our Milky Way but shine hundreds of times fainter.

The first stars ignited from clouds that contained nothing but hydrogen and helium. Heavy elements (carbon, oxygen, iron) came later, forged inside stars. But among those pioneers, there could have been lightweight stars, with masses just below that of the Sun.

Hidden in the dense swarm of stars at the center of the Milky Way lies the globular cluster Tonantzintla 2. It went unnoticed for decades, yet it holds the key to the earliest history of our galaxy.

In the infant universe, right after the Big Bang, space was expanding rapidly, and the vacuum resembled a superheated liquid. When 'boiling' began, bubbles of true vacuum emerged. Expanding at the speed of light, they triggered gravitational waves — tremors of space itself that have reached us.

A few hundred million years after the Big Bang, the universe resembled an endless dark ocean, shrouded in a thick fog of neutral (non-ionized) hydrogen. Then something dispersed the gloom: ultraviolet radiation knocked electrons out of atoms, making the gas as transparent as pure water.

After the Big Bang, the universe was hot and dense. In clumps of dark matter, invisible stuff felt only through gravity, its particles, colliding, annihilated, giving birth to powerful radiation. This hidden heat, like an invisible furnace, warmed gas clouds from within.