Plasma

Interestingly, in physics, plasma is the often overlooked fourth state of matter, aside from solid, liquid and gas. Plasma is ionized gas containing free electrons, making it responsive to electromagnetism, and conductive of electricity, in turn enabling it to take a very visible physical shape unlike other forms of gas. The stars are made of plasma; so is lightening and the Northen Lights (Aurora Borealis). Plasma display screens also basically employ this effect.