Definition : Electromagnetic radiation emitted by matter due to its temperature \rightarrow the shape of the spectrum is mainly determined by temperature and it follows the Blackbody spectrum

Mechanism : It arises from the random thermal motion of charged particles in matter, especially electrons, which accelerate during collisions and emit electromagnetic waves.

• In opaque matter, emitted photons are repeatedly absorbed and re-emitted until the radiation field comes into thermal equilibrium with the material. That is why a dense astrophysical object can produce a smooth, continuous spectrum rather than discrete emission lines.