act

Imagine looking at a distant mountain range through morning fog. The peaks' outlines are blurred, and if the fog is patchy, some slopes fade more than others. That's roughly how astronomers see the ancient light of the universe, which has been traveling to us for 13.8 billion years. This light was born when the universe was just 380,000 years old, long before the first stars.

The night sky is full of deceptive lights. Astronomers were searching for galaxies that ignited in the first few hundred million years after the Big Bang: their light has traveled to us for nearly 13 billion years. Six faint smudges were selected from images taken by the Hubble and Spitzer space telescopes.

The explosion of a massive star is not just a flash: it's a blow to the surrounding gas. But until now, no one had looked at how the gas itself moves at the sites of such explosions. Now astronomers have gathered data on 33 nearby supernovae and for the first time measured the turbulence of the cold molecular gas around them.

Betelgeuse, the red supergiant familiar from Orion's shoulder, keeps surprising us. After the mysterious Great Dimming of 2019–2020, when the star suddenly dimmed, it didn't just recover; it changed its ways.

0.965—a number that split cosmologists into 'before' and 'after'. That's the value of the spectral index ns measured by the ACT telescope as it stared into the cosmic microwave background — the cooled light of the Big Bang.

380 thousand years after the Big Bang, the universe cooled enough for light to decouple from plasma. That cosmic microwave background still pervades space, like the first chord of a symphony, the echo of a fiery beginning.

The universe sounds with silence. The lion's share of matter — about 85%—remains invisible, manifesting only through gravity. Back when Vera Rubin Vera Rubin showed that galaxies spin as if wrapped in unseen mass.

The cosmological debate is like two craftsmen measuring the same wall but getting different lengths. One uses a tape measure, applying it to nearby landmarks — Cepheids (pulsating beacon stars) and Type Ia supernovae (flashes of dying stars). He finds the wall is stretching at 73.5 arbitrary units.

When a giant planet grows, it pulls in gas. Some of that gas swirls around it into a small disk — called a circumplanetary disk. It is in such disks that moons are thought to form. For the planet PDS 70 c, located 370 light-years away, such a disk was directly observed using the ALMA antenna array in the millimeter range.

Cosmology is like an orchestra where different sections suddenly start playing out of sync. Measurements of the universe's expansion rate (the Hubble constant) from the early and late universe give different numbers.

The cosmic microwave background is the petrified light of the first moments. Shortly after the Big Bang, microscopic quantum fluctuations were stretched by inflation to the scales of galactic superclusters.

The Universe at 700 million years old was a noisy construction site, just beginning to light up. Telescopes caught a signal from that distant epoch: the galaxy REBELS-25, massive and full of stellar fuel.

Dark matter is an invisible substance that reveals itself only through gravitational effects: it bends the light of distant galaxies, much like an unseen window that alters the path of light rays.

380,000 years after the Big Bang, the universe had cooled enough for scattered particles to combine into hydrogen atoms.

Cosmology is the music of the spheres, and the Hubble constant once seemed like a reliable metronome.

A compressed spring can sit for years without moving. It seems frozen forever, but inside the metal, atoms slowly rearrange, and one day the spring clicks, settling into a new, more relaxed position.

The cosmic microwave background is the afterglow of the Big Bang, which we see at millimeter wavelengths. But it also has a long-wavelength tail extending into the radio range.

A magnifying glass focuses sunlight into a bright point. If the glass has a tiny flaw, the spot of light becomes distorted. Gravitational lensing works in a similar way: a massive galaxy bends light rays from a more distant source, creating an enlarged and sometimes distorted image.

Imagine a huge layered cake, where the layers of dough are space and the filling is a special region resembling an invisible wall. This wall is not made of bricks but of energy, and it could be as thick as the entire universe. If such a wall exists, it should stretch the dough layers differently: those lying along it spread apart faster, while those across it spread slower.

Ancient light, traveling 14 billion years, reaches us from all directions. At first glance, it looks perfectly smooth, but if you look closely, tiny fluctuations appear, like ripples on a still pond. Those ripples aren't random noise; they're an encoded history of the universe.

Moving clumps of galaxies and invisible dark matter create wakes in the afterglow of the Big Bang, like boats stirring a pond. This wake, the moving lens effect, is so subtle it shifts the light’s temperature by only a few millionths of a degree: comparable to detecting a candle’s heat from across a continent.

A dust storm that has raged for millions of years is not in a desert but between the stars. There, clouds of tenuous gas drift, threaded by magnetic fields. These fields align dust grains like compass needles along field lines. When such dust emits, its light becomes polarized: it oscillates in a single plane, like a rope shaken only up and down.

Two clocks tell different times. One sits on our desk, the other lies far in the past, in the glow left over from the Big Bang. The first, looking at nearby galaxies, ticks off the expansion rate of the universe — about 73 kilometers per second per megaparsec of distance. The second, peering into ancient light, gives a noticeably lower value — roughly 67.

The cosmological dispute resembles two craftsmen measuring the same room with different tape measures. One, looking at distant galaxies, gets one number. The other, peering into the ancient glow (the cosmic microwave background, the cooled light of the Big Bang) gets another, smaller number.

In a dense cloud of gas and dust where giant stars are born, the ALMA telescope has spotted something familiar. Four thin gas jets shoot out from the same region, each leaving behind a chain of bright knots, like a dashed line.

Cosmologists have measured how fast distant galaxies are receding in different parts of the sky. To do this, they used two kinds of "cosmic rulers": galaxy clusters and a certain type of supernova explosion. Both methods showed the same thing: in one direction, the Universe is expanding slightly faster than in the opposite direction.

A giant magnifying glass made of gravity zoomed in on a distant galaxy, and astronomers got a peek into its chemical kitchen.

Light that has traveled to us for nearly 14 billion years is like an old photograph whose details emerge with careful processing. The cosmic microwave background (the afterglow of the Big Bang) holds the imprint of the universe's first moments, but its signal is faint and distorted.

Astronomers are trying to capture the radio echo of the Big Bang — a faint glow that fills the entire universe. But the receiver is choking with noise: our Galaxy is packed with glowing interstellar dust, whose emission can easily be mistaken for a signal from the distant past.

In the Andromeda galaxy, our Milky Way's nearest large neighbor, astronomers have spotted giant cold clouds where stars are born. These clouds are made of gas and dust, but seeing them directly is tricky: they barely shine.

In its first moments, the universe resembled dough beginning to rise. If the yeast is unevenly distributed, the rolls come out in different sizes. Astronomers are hunting for such 'clumps' in the oldest light and in the arrangement of galaxies to understand what the recipe was.

Light from a streetlamp passing through blinds flickers: the stripes shift, and brightness rises and falls. From that rhythm, you can guess how wide the lamp is. The new method for measuring stars works similarly: instead of capturing a sharp image, astronomers monitor the "twinkling" of light collected by two or more telescopes simultaneously.

The night sky glows not only with stars. Between them lies a faint microwave radiance that astronomers have noticed for three decades but couldn't explain. One idea: the culprits are polycyclic aromatic hydrocarbons — molecules like tiny soot flakes that spin in space and, like miniature antennas, emit radio waves.

In cold clouds of interstellar gas, carbon hides inside carbon monoxide (CO) molecules, like sugar dissolved in tea. But near hot, massive stars, this 'tea' boils: harsh radiation tears the molecules apart, and carbon escapes as lone atoms or ions.

A hair dryer aimed at a block of ice strips vapor and droplets from its surface, and the ice slowly melts. The wind from the center of our Galaxy works in much the same way: it picks up cold gas clouds and carries them away, heating and shredding them along the way. Astronomers decided to systematically search this flow for molecules, the coldest and densest form of gas, for the first time.

The universe is a pie baked from a single recipe, but the teaspoon and the kitchen scale stubbornly show different amounts of sugar. That’s how it is with the expansion of the universe: measurements from nearby stars (the spoon) give one number, while those from the ancient light of the Big Bang (the scale) give a completely different one.

Two methods of measuring the Universe's expansion rate yield conflicting results. Measurements from supernova explosions, carried out by Adam Riess's team, show faster expansion than data from the cosmic microwave background — the light left over from the Big Bang.

The ACT telescope in Chile's Atacama Desert stared at the sky from 2007 to 2022. Its target: the cosmic microwave background, light that has been traveling toward us for 13.8 billion years. This light is polarized: its waves oscillate in specific planes, like strings stretched in different directions.

The Atacama Desert in northern Chile is the driest non-polar place on Earth. The sky is almost always clear, and the air is so devoid of moisture that even distant galaxies are visible without interference.

Every night, an invisible sentinel hangs over the Andes. The GOES-12 satellite, and later its successor GOES-13, watches Earth from an altitude of 36,000 kilometers, recording how the mountains breathe clouds. For five straight years, it tracked where the sky stayed clear and where it got wrapped in cotton.