Plasma Is the Most Common Form of Matter in the Universe — and You See It Every Day

The Forgotten Fourth State

Solid, liquid, gas — these are the states of matter most people encounter in everyday life, and they dominate introductory chemistry and physics curricula. But there is a fourth state that vastly outnumbers all three combined: plasma. Plasma is a state in which matter has been heated to such high temperatures — or exposed to such intense electromagnetic radiation — that electrons are stripped from their atoms, creating a fluid mixture of free electrons and positively charged ions. Unlike neutral atoms in a gas, the components of a plasma are electrically charged, giving plasma distinctive electromagnetic properties.

More than 99 percent of all visible, ordinary matter in the universe exists as plasma. Every star in the night sky is a plasma. The hot, tenuous gas filling the space between galaxies is a plasma. The vast nebulae from which new stars are forming are mostly plasma. Earth is surrounded by plasma in the form of the Van Allen belts. Even lightning — the brief and violent discharge of atmospheric electricity — is a bolt of plasma, its channel superheated to temperatures around 30,000 kelvin, roughly five times hotter than the surface of the Sun.

What Makes Plasma Different

In a neutral gas, atoms move independently and interact primarily through brief collisions. In a plasma, the free charges generate and respond to electromagnetic fields, meaning that the behavior of one part of the plasma is coupled to distant parts through long-range electromagnetic interactions. This gives plasma collective behaviors — waves, instabilities, oscillations, and structures — that have no analog in neutral gases.

Plasma can be confined, accelerated, and shaped by magnetic fields, a property that is central to the design of fusion reactors. Plasma can generate its own magnetic field through the motion of its charges — a process called the dynamo mechanism, which is responsible for generating the magnetic fields of Earth, the Sun, and other astronomical bodies. When plasma from the Sun — the solar wind — interacts with Earth's magnetic field, the result is the aurora borealis and aurora australis, shimmering curtains of light produced as energetic particles excite and ionize molecules in the upper atmosphere.

Plasma in Stars

The most familiar and important plasma in the universe is the stuff of which stars are made. Inside a star like the Sun, temperatures reach about 15 million kelvin at the core, far exceeding the threshold for complete ionization of hydrogen. In this environment, hydrogen nuclei — bare protons — and helium nuclei are free to move at enormous velocities, colliding with sufficient energy to drive nuclear fusion reactions.

The plasma state is essential to stellar fusion. Because the protons are not bound in neutral atoms, they can approach each other closely enough for the strong nuclear force to fuse them together. The energy released by these fusion reactions — ultimately the energy of sunlight — heats the surrounding plasma and generates the radiation pressure that prevents the star from collapsing under its own gravity. A star is, in thermodynamic terms, a plasma held in balance between gravity and the outward pressure of the fusion it sustains.

Plasma on Earth

Beyond lightning and aurora, plasma appears in numerous human technologies. Neon signs and fluorescent lights work by running electrical current through a gas at low pressure, ionizing it into a plasma that emits characteristic wavelengths of light. Plasma television displays used grids of tiny plasma cells to produce images. Plasma torches — industrial tools that generate temperatures above 10,000 kelvin — are used for cutting metal, spraying heat-resistant coatings, and treating hazardous waste. And plasma physics is at the heart of nuclear fusion research: experimental reactors like ITER in France aim to confine hydrogen plasma at temperatures exceeding 150 million kelvin — ten times hotter than the Sun's core — long enough to achieve sustained net energy from fusion, potentially transforming global energy production.