You are likely familiar with the 3 states of matter which we encounter during our everyday lives: solids, liquids, and gases. Yet there is a fourth state of matter less often encountered: plasma. Plasma makes up all of the stars, and is the most common form of matter in the visible universe. To understand plasma, let’s first quickly review the properties of the other states of matter.
A solid typically consists of a large number of atoms which are bound together with some definite structure. Now if we add enough energy (heat) to a solid, our experience tells us that it will melt and eventually become a liquid. In this state, the atoms only loosely interact with each other and the liquid is able to flow. Now if we once again add enough energy to the liquid, it will become a gas. In a gas, the atoms are totally free to “wander” around and, as a result, they will fill any container that they are put into. Next is where plasma comes in. If we have a gas that consists of single atoms, and we add sufficient energy (heat) to it, the negatively charged electrons which are typically bound to the positively charged nucleus of these atoms will overcome the pull of the nucleus (opposite charges attract). The result will be a “soup” of particles consisting of the free electrons (- charge) and the free nuclei (+ charge). This state is known as plasma. Fusion reactions require so much energy that they must occur with the hydrogen isotopes in this plasma state.
Since plasmas are made of charged particles every particle can interact with every other particle, even over very long distances. This makes plasmas behave very strangely compared to the other states of matter. When every particle “talks” to every other particle the material can form all sorts of waves and move in many complex ways. This makes studying plasmas very interesting and hard to do. The fact that 99% of the universe is made of plasmas makes studying them very important if we are to understand how the universe works. Lessons learned in plasma experiments on Earth can tell us things about how distant stars work.
Some examples of plasmas are:
- The glowing “gas” (actually plasma!) inside neon signs and fluorescent lights.
- The glowing parts of a plasma TV.
- The exhaust of big rockets.
- The northern and southern lights.
- The solar wind and space weather.
- The Sun and all the stars.
- The stuff inside a fusion reactor.
Next: Why Fusion?