Magnetic radiation effects describe how magnetic fields alter the behavior of electromagnetic radiation — changing its polarization, intensity, direction, or even the probability of photon emission. In astrophysical contexts, strong magnetic fields around neutron stars or magnetars can bend light paths, split spectral lines, and produce exotic phenomena like vacuum birefringence. These effects are also crucial in laboratory plasma physics, where magnetic fields confine and shape radiation from charged particles.
History
The theoretical foundations were laid by Hendrik Lorentz and later developed by quantum electrodynamics in the 1930s; the first observational evidence of magnetic effects on starlight polarization came in the 1940s.
How it works
When photons travel through a magnetic field, they can interact with virtual electron-positron pairs that the field polarizes, causing the vacuum itself to act like a crystal with different refractive indices for different polarizations. This leads to effects like Faraday rotation, where the polarization plane rotates, or Cotton-Mouton effects in plasmas. In emission, magnetic fields force charged particles to spiral, producing synchrotron radiation with characteristic polarization and spectrum. Strong fields can even suppress or enhance certain quantum transitions, altering the emitted photon energies.
In practice
Used in plasma diagnostics in fusion reactors, in astrophysical measurements of cosmic magnetic fields via polarization, and in the design of synchrotron light sources for materials science.
Fun fact
Magnetars — neutron stars with magnetic fields a thousand trillion times stronger than Earth's — can bend X-rays so much that photons emitted from one side of the star become visible from the other side.
Two dancers on one stage: one pulls the partner in one direction, the other in the opposite. In the crystal Cu2(OH)3Br, known as botallackite, copper atoms form chains where the spins (magnetic moments) of neighboring ions align either parallel, as in a ferromagnet, or antiparallel, as in an antiferromagnet.
Light born when a fast electron enters a material is usually assumed to be the same in all directions. But in crystals where optical properties depend on direction, that's not the case. Run your hand over velvet: one way it's smooth and shiny, the other — dark and rough. Similarly, a crystal responds differently to light depending on how it's oriented.
Light from the hottest stage of the universe has been traveling toward us for nearly 14 billion years. This is the cosmic microwave background — a faint glow filling the entire sky.
10¹⁵ Gauss — that's the magnetic field found on some white dwarfs. It is billions of times stronger than what a compass shows on Earth. A white dwarf is not a star in the usual sense, but a cooled core the size of a planet. Inside, gravity opposes the pressure of degenerate electrons.
A lighthouse at sea doesn't just rotate: its lamp itself dims and brightens on its own. Magnetic white dwarfs, the ultra-dense remnants of stars like our Sun, behave in much the same way. Their powerful magnetic fields can convert light into axions — hypothetical particles that could explain the Universe's hidden mass.
The flash lasts a thousandth of a second, but in that instant it releases as much energy as the Sun emits in a day. Such signals, fast radio bursts, have been caught by telescopes since 2007, and their source remains a mystery. A new study offers an elegant answer: it's all about a cosmic amplifier.
The Sun is not just a source of light but a giant laboratory where ghostly particles are born. Every second, billions of neutrinos fly through your body, barely noticing you. But inside the Sun, these particles behave differently: they change their type on the fly, like an actor playing three roles in a single play.
A dead star with a magnetic field billions of times stronger than Earth's is a magnetar. Its crust cracks, sending a powerful X-ray burst into space. But some of that light doesn't reach us in its usual form. In an ultra-strong field, photons can turn into gravitational waves — the trembling of space itself.
A child on a swing: too strong a push and they fly off. Roughly this is how powerful light tears electrons out of an atom. It would seem that the stronger the push, the more certain the destruction. But in the quantum world it is different: when the field strength crosses a certain threshold, the atom suddenly freezes.
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.
Two neutron stars (the remnants of dead stars, compressed to the size of a city but weighing as much as the Sun) spiral around each other and eventually collide. At that moment, something between a black hole and a super-powered magnet is born: a field billions of times stronger than that of the most powerful MRI machine.
A flashlight beam glides over uneven glass. The glass is massive galaxy clusters, and the flashlight is ancient light born shortly after the big bang. Passing by such clusters, light doesn't just bend around them like water around a rock. Its path shifts slightly sideways, and the amount of shift depends on how the light is 'twisted'—right or left.
Neutron stars are the ultra-dense remnants of stars, where matter is compressed to the limit described by Subrahmanyan Chandrasekhar. Magnetars are a type of neutron star with a magnetic field a quadrillion times stronger than Earth's.
The Universe speaks two fundamental languages — gravity and light. Under normal conditions, they do not mix: gravitational waves glide through matter without a trace, while photons dance in mirror labyrinths.
A neutron star is the collapsed core of a massive star, squeezed to the size of a city. In its heart, matter is packed so densely that atoms cease to exist, and protons and neutrons dissolve into a sea of quarks.
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.
Neutron stars are the compressed cores of dead stars — city-sized objects with staggering density. Some of these stars become pulsars, cosmic lighthouses emitting strictly periodic radiation pulses.
A magnetar is a neutron star with a magnetic field hundreds of millions of times stronger than Earth's. If you brought an ordinary magnet near such a field, it would instantly lose its magnetism, and atoms would stretch into thin filaments.
You can make a light beam look like a flower with several petals. If you send such a beam through a cloud of cold rubidium atoms and switch on a magnetic field, the petals start to rotate. The angle of rotation is directly linked to the field's strength.
A neutron star is a city the size of a metropolis squeezed into a small asteroid. Around it, plasma, a gas of charged particles, seethes, and waves ripple through it like ripples on a pond. There are three kinds of waves: Alfvén (A), ordinary (O), and extraordinary (X).
In the dark cloud L43, where stars are born, dust grains twirl like tiny compasses. Light from a young star pushes them, while the magnetic field lines them up in a specific direction. When a grain is turned sideways to us, its heat reaches us polarized, like light passing through a narrow slit.
Light from the star HD 163296 passes through the surrounding gas-and-dust disk like a flashlight beam through murky water. The disk's particles scatter the light, giving it a special property — polarization: the waves begin to oscillate in a single plane, like a rope shaken strictly up and down.
The crystal Ca2RuO4 resembles a stack of thin sheets. Inside each sheet, the electron spins are arranged in strict order, like rows of soldiers on a parade ground. The bonds between the sheets are weak, and their sign can be flipped by slightly pulling the crystal apart.
A beam of circularly polarized light hits a MAPbI3 perovskite crystal. The electrons inside start behaving like tiny spinning tops, their axes aligning along the beam. This phenomenon is known as optical spin orientation.
A football kicked with spin doesn't fly straight: it bends to the side. A tightly focused beam of light does something similar: it starts pushing an atom not just forward but also sideways. Physicists measured this shift on a single calcium ion trapped in a light trap.
The beam was aimed at the atom like a spotlight on a grain of sand.
Magnetic materials can store oscillatory energy, like a tuning fork that keeps ringing after being struck. When such a material is placed in a microwave cavity, its oscillations (magnons) start interacting with light (photons).
A laser beam hits a shiny crystal, and comes back different: slightly shifted in color, with a different polarization. In a magnetic field, this transformation of light becomes especially noticeable.
An ordinary magnetic compass freezes when lightning strikes nearby. A sudden jump in the magnetic field throws the needle off. A similar problem has been hindering scientists trying to measure magnetism in strong pulsed fields: those that switch on for a thousandth of a second.
The new setup tackles this with a laser beam.
In a dark room, two flashlights shine on a wall. Usually, their beams simply add up, and the spot becomes brighter. But if the flashlights emit light in special packets, photons, then under certain conditions they can behave differently. Instead of independently hitting different spots, two photons 'agree' and only come out together, as a pair, from a single output.
Astronomers have been wrestling for years with the mystery of fast radio bursts — ultra-short yet incredibly powerful radio signals from distant galaxies. Some flash repeatedly, like beacons with an irregular rhythm, while others are detected only once, leaving behind nothing but questions.
Light from distant galaxies passes through telescope lenses like through a stack of window panes. Each pane is coated with a thin film to reduce glare. But this film acts as a polarizing filter: one component of the light wave passes a bit more freely, the other a bit worse. As a result, the wave rotates slightly, and the telescope sees a different picture than what is in the sky.
A magnetar is a neutron star with a magnetic field a quadrillion times stronger than Earth's. Sometimes it ejects a blob of plasma, like a tiny balloon with thousands of invisible springs bouncing around inside.
In 1936, two physicists, Werner Heisenberg and Hans Euler, poring over the equations of quantum electrodynamics, found something strange. In a sufficiently strong magnetic field, vacuum should cease to be empty.
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 ARCADE2 radiometer on a high-altitude balloon detected an excess radio emission, while the ground-based EDGES experiment found an anomalously deep trough in the hydrogen spectrum at 21 cm. Both signals do not fit the standard cosmological model and point to an unknown source of soft photons.
Cosmic rays are atomic nuclei accelerated to near-light speeds. They arrive at Earth from all directions, and their composition tells us what's happening in the far reaches of the Galaxy.
