supernova cosmology

Gamma rays are the most energetic light in the Universe. But one part of them, the medium-energy range, long remained invisible: instruments couldn't catch them, leaving a gaping hole in the sky. Scientists call it the "MeV gap," named after the unit of energy these rays carry. The new camera works like a three-layer detective.

The universe is constantly sending us signals, but many are too faint to notice. Relic neutrinos, particles left over from the Big Bang, pass through Earth by the billions every second, yet catching even one is a feat on the edge of possibility. We need a detector that can sense energy a thousand times smaller than what it takes to move a speck of dust.

Six runners sprint down the track, and officials time their speed without noticing a tailwind. The wind blows at their backs, and the stopwatches show a better result than the truth. Roughly this is how six megamasers — natural cosmic lasers in distant galaxies — misled astronomers measuring the expansion rate of the universe.

Measuring distances in the universe is no easy task. Almost all methods rely on light, which can be absorbed by dust, scattered, or distorted along the way. It's like trying to spot a distant lighthouse through fog and haze. Neutrinos are a different story. These ghostly particles pass through anything without noticing obstacles.

The universe is a vast, dark ocean. We see only the glowing foam on its surface — stars and galaxies. But hidden in the depths are two invisible forces: dark matter, which with its gravity keeps galaxies from flying apart, and dark energy, which, on the contrary, pushes space itself apart, making the universe expand faster and faster.

In 1998, physicists caught neutrinos doing something astonishing: the particle changes its type on the fly. That is only possible if it has mass. This became the only laboratory proof of physics beyond the Standard Model. But exactly how much a neutrino weighs remains a mystery.

A massive star exhausts its fuel, and its core collapses in a fraction of a second. A supernova is born, along with a brief but powerful shower of neutrinos. These particles barely interact with matter, so they fly away freely, carrying information about the catastrophe.

Cosmology has landed in an interesting pickle. The two main ways to look back into the universe's past, via the early glow (the cosmic microwave background) and via later objects like supernovae, yield different numbers for the expansion rate (the Hubble constant) and for how clumpy matter is distributed.

The hunter of ancient light, the James Webb Telescope, aimed its mirrors at a tiny patch of sky and caught a strange beacon. The object, with the working name beacon_1420-$$5253_{4770}$$, flashed and faded. At first, it was logged as a candidate for the most distant galaxy, as if we were seeing it just 300 million years after the big bang.

A drama is brewing in cosmology: two principal musical instruments, the orchestra of the early Universe and the chamber ensemble of the modern cosmos, play the same symphony of expansion at different tempos.

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 cosmological orchestra doesn't tune to a single tuning fork. There are two groups of instruments: one listens to the hum of the young universe — the cosmic microwave background, while the other reads notes from mature galaxies and supernovae.

The Universe resembles a dense forest: up close, individual galaxy-trees are visible, gathered into groves, but from a distance everything merges into a solid green canopy. The boundary beyond which the cosmos becomes homogeneous is called the angular scale of homogeneity: it's the size of a patch of sky from which galaxies are distributed evenly.

Type Ia supernovae are the final, blinding chords in the symphony of stellar evolution: when a white dwarf crosses the limit predicted by Chandrasekhar, it explodes so brightly that for a moment it outshines an entire galaxy.

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

Cosmologists staged a showdown between two kinds of cosmic explosions. Type Ia supernovae are stars that flare up with nearly identical brightness, making them reliable beacons for measuring distances across the universe.

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.

Imagine inflating a balloon. It expands quickly at first, then slows down, and then suddenly speeds up again, as if someone gave the pump another squeeze. That's what seems to be happening to our universe.

Neutrinos are the most abundant massive particles in the universe. Trillions of them pass through us every second, yet they leave barely a trace. Their collective gravity, though tiny, can influence the motion of entire galaxies. Think of two people approaching each other on a busy street; invisible passersby alter their speed.

Conventional dark matter detectors are like a soccer goalkeeper waiting for a powerful shot while the ball barely rolls. The invisible particles filling our galaxy often move too slowly to be noticed by sensitive sensors.

The universe keeps a tally of every newborn star. Over 13.8 billion years, galaxies have ignited so many stars that their 'census' can reveal the nature of the cosmos itself, just as tree rings reveal past climates.

Take two heavy balls and place them a meter apart: they attract each other with a force that weakens by a factor of four when you double the distance. Newton discovered this law, and it works in a room, in the solar system, in a galaxy. But does it still hold when we're talking about hundreds of millions of light-years? Astronomers found a way to test this directly.

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.

Superbubbles are cosmic giants, akin to soap bubbles, but instead of soap film, they contain rarefied interstellar gas, and they're inflated not by a breath but by a series of supernova explosions. In computer simulations, they behave like living things: they grow, cool, and move. But until now, we couldn't precisely trace their boundaries.

When a massive star explodes, its remnants fly apart like fragments of fireworks. But how do we know how far away such an explosion occurred? Astronomers have found a way: they look at the gas clouds that these remnants collide with. The idea is simple. Supernova remnants are often surrounded by clouds of cold molecular gas.

Dark energy is usually seen as an innate property of the cosmos, at work from the very first moments. But a new model suggests it behaved like water on the verge of boiling: long unnoticed, then suddenly kicking in at a critical moment. This scenario is called 'late activation': around 5–7 billion years ago, a shift occurred, and the universe’s expansion began to accelerate.

Cosmic rays are charged particles that constantly bombard Earth from deep space. When one of these particles enters the atmosphere, it collides with air nuclei and spawns a whole cascade of secondary particles: electrons, muons, photons.

A distant galaxy birthing hundreds of stars should glow in oxygen. That's what astronomers thought: hot young stars heat the gas, which then emits a characteristic infrared glow at a wavelength of 63 microns. It's like steam rising from a boiling pot — a sure sign of vigorous activity.

Light from a distant star travels to us for billions of years, and during that time the universe has time to expand. How can we check that we correctly understand this journey? Astronomers use two 'rulers': supernova explosions, which shine with a known brightness, and fast radio bursts — short, powerful pulses of radio waves from other galaxies.

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.

When a distant star explodes, its light travels toward us for billions of years. Astronomers measure how dim it appears and use that to calculate the distance. Usually, this involves complex models with dark energy and other mysteries.

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.

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.

Type Ia supernovae are the 'standard candles' of cosmology: their peak luminosity is nearly identical, allowing distances to be determined from apparent brightness — the fainter the object, the farther away it is.

Astronomers use Type Ia supernovae — thermonuclear explosions of white dwarfs — as 'standard candles': their peak luminosity was long thought to be the same everywhere in the universe.