stellar nucleosynthesis

An interpreter gets distracted by every rustle in the hall, and a one-hour meeting stretches into two. A neutron star compresses a solar mass into a sphere the size of a city, and the matter in its core is denser than an atomic nucleus. Physicists cannot probe its structure in the lab: the required pressures are unattainable.

A neutron star is the remnant of an exploded star, compressed so tightly that a teaspoon of its material would weigh as much as a mountain. Inside such an object, protons and neutrons are packed tightly together, and under enormous pressure, hyperons, particles containing a strange quark, can appear.

In dark interstellar clouds where new stars are born, chemistry starts with a tiny particle — the trihydrogen ion (H₃⁺). It collides with other atoms and sets off a cascade of reactions that build ever more complex molecules. For a long time, it was thought that the main reaction producing it, H₂⁺ colliding with H₂, only happens in the gas phase.

A handful of sand in your fist: the grains press against each other, and your hand can't squeeze any further. Ordinary matter behaves similarly. But in a neutron star, compression is billions of times stronger — atoms are crushed, electrons are squeezed into protons, and nearly all space is filled with neutrons.

In June 2024, the CHIME radio telescope recorded over 700 radio bursts per hour from source FRB 20240114A. Such a hyperactive repeater releases in one hour nearly all the magnetic energy of a typical magnetar (a neutron star with an ultra-strong field).

When two neutron stars, the ultra-dense cores of dead stars, collide, a kilonova is born: an explosion a thousand times brighter than a typical nova. This is the universe's true smelting works. In the scorching cloud racing outward at near-light speeds, a furious flux of neutrons transmutes atomic nuclei into gold, platinum, osmium.

Two neutron stars whirl in their final dance. If their spin aligns with their orbital motion, the partners merge neatly, launching a narrow jet of superheated matter. If they spin in opposite directions, the dance breaks apart, scattering a thick shroud of debris.

In 2017, detectors picked up a tremor in space — gravitational waves from the merger of two neutron stars. Telescopes immediately found a flash of light: a cosmic explosion astronomers dubbed a kilonova. In that fiery cauldron, it turned out, the heaviest elements of the periodic table are born — gold, platinum, uranium.

In the first moments after the Big Bang, matter and antimatter should have been created in equal amounts. But today we see only matter — stars, planets, ourselves. Where did the antimatter go? One clue hides in nearly elusive particles: right-handed neutrinos. The usual story is that their decays create a slight bias in favor of matter.

Inside a neutron star, the density doesn't change smoothly but drops abruptly at sharp cliffs — density staircases. At these steps, the void suddenly births pairs: neutrinos and antineutrinos.

In cold clouds between the stars, dust grains are coated with ice, like windows covered with frost in winter. On this icy crust, chemical reactions take place that do not occur in gas. One such reaction is the encounter between a carbon atom and a nitrogen molecule.

Deep inside a massive star, before it explodes, layers sit on top of each other like the layers of an onion. Sometimes two adjacent layers, the carbon and oxygen layers, mix together. It's like how layers of broth and vegetables in a pot of soup blend when you stir them with a spoon.

Deep inside a dying star, just before it goes supernova, nuclear reactions determine which chemical elements will be scattered across the cosmos. One such reaction is the collision of an oxygen nucleus with a proton, producing a nitrogen nucleus and an alpha particle (a helium nucleus).

When a star like the Sun runs out of hydrogen, it swells into a red giant, and helium piles up in its core. At some point, the helium ignites — in a few seconds, it releases as much energy as the star had radiated over thousands of years. This is a helium flash.

In the dark, cold clouds where stars are born, dust grains are covered with an icy crust. Across this crust, like on a winter road, individual atoms wander slowly. Calculations show that it is precisely these wandering oxygen and nitrogen atoms that kick off the assembly of the HNSO molecule — a compound of hydrogen, nitrogen, sulfur, and oxygen.

Sub-Neptunes — worlds slightly smaller than Neptune — are common among exoplanets. They are detected using the transit method (by the dimming of a star), pioneered by William Borucki.

The most common type of planet in our Galaxy — rocky worlds around other stars, or exoplanets, shrouded in the simplest gas hydrogen. Their innards remained a mystery until scientists recreated the conditions of the interior in the lab.

At the center of galaxy NGC 1600, 200 million light-years away, astronomers spotted a dense cluster of stars. It looked like a bright knot against the diffuse glow, and that was unexpected.

In 2017, the LIGO and Virgo detectors caught gravitational waves from the merger of two neutron stars. A kilonova flared: a brilliant cosmic explosion thought to forge the heaviest elements in the periodic table. Gold in jewelry, platinum in catalysts, europium in smartphone screens: all of it, according to a beautiful legend, came to us from such catastrophes.