Star in microwave

The electromagnetic fields generated by the microwave pull electrons from their nuclei. If electrons are floating around freely, even for a very short amount of time, they can travel far away from their point of origin. As they move, they crash into air molecules in the oven, and can knock electrons in them to higher-energy orbits. Then these electrons fall back, emitting light. That's why you have a glowing blob of plasma over your flame. This plasma is hotter than the rest of the air, and so it tends to rise up to the top of the microwave.

Plasma is the fourth state of matter. Many places teach that there are three states of matter; solid, liquid and gas, but there are actually six. The fourth is plasma (the fifth is Bose-Einstein condansate and the sixth is Fermi-Dirac condensate). To put it very simply, a plasma is an ionized gas, a gas into which sufficient energy is provided to free electrons from atoms or molecules and to allow both species, ions and electrons, to coexist. Plasma becomes conductive and it responds to electrical and magnetic fields opposite to gas it is also the most common state of matter in the universe (stars are made of plasma).