neutron

A neutron confined in a nucleus behaves differently from a free one. Its gluon cloud, which holds quarks together, compresses like a spring under load. Previously, this could only be assumed, but now physicists have directly observed the effect for the first time. At Jefferson Lab, an electron beam struck liquid deuterium, knocking photons out of the nuclei.

In nuclear physics, a puzzle has long been nagging: why among elements lighter than bismuth, only technetium (No. 43) and promethium (No. 61) have no stable isotope at all? All their neighbors in the periodic table can boast at least one long-lived variant, but these two seem to fall out of the general pattern.

In a quiet room, you can hear the faintest whisper. Likewise, in the hydrogen atom, the lightest of all, an uninvited guest is easier to spot. That guest could be the Z' boson, a mediator particle of a new force predicted by many unification theories. The Standard Model already has its own mediator — the Z boson.

The interiors of neutron stars are a realm of degenerate matter. Here, protons condense into a superconducting condensate, threaded by quantum vortices. Imagine tiny magnetic tops: each carries a quantum of magnetic flux and glides through the electron fluid.

At first glance, the atomic nucleus is a cramped communal apartment where protons and neutrons (together called nucleons) live by strict rules. Each occupies its own orbit, like electrons in an atom, and on average everything looks orderly.

The atomic nucleus is not a solid ball but a dense swarm of tiny particles called quarks, glued together by a special glue (the strong force). In light nuclei, such as calcium, this swarm is simply arranged: the numbers of the two quark types, up and down, are almost equal, like the white and black keys in an octave.

To uncover the proton's true size, physicists swapped the electron in a hydrogen atom for its heavy copy — the muon. Acting like a magnifying glass with thousandfold power, the muon gets right up against the nucleus and 'probes' the proton with unprecedented precision.

If an atomic nucleus is a family, then in an ordinary helium house live two protons and two neutrons, holding hands tightly. Now imagine that one family member is an oddball who loves to wander far from home.

In the first minutes of the Big Bang, the universe whipped up a cocktail of hydrogen, helium, and a pinch of lithium.

Inside a piece of magnetic material, electron spins, tiny magnetic arrows, usually arrange into simple patterns. Sometimes they swirl into vortices, like water down a drain, and these vortices can tie themselves into knots.

Uranus and Neptune have long puzzled scientists: their magnetic fields are heavily tilted and tangled, nothing like Earth's. The answer lay in an exotic form of water — superionic ice, which fills their interiors.

Light consists of portions — photons. Max Planck was the first to understand that light is emitted in quanta. Today, we can guide single photons. When such a photon encounters a fast shutter, it cannot be sliced — half a photon doesn't exist. Instead, a quantum mixture of states with different photon numbers emerges: zero, one, two, three..

In 1976, Gerard 't Hooft noticed that the vacuum of a gauge theory is not as simple as it seems: it possesses a topological structure that manifests itself in a nonzero topological susceptibility.

High above the Antarctic ice sheet, a balloon with a detector floated for twenty days. It caught tiny particles that had been traveling toward us for millions of years from distant stellar explosions. Now scientists have sorted through the catch and reported how much energy the protons and nuclei of different elements carried.