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Why do hot objects emit electromagnetic radiation across a range of frequencies?

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Diagram of a tree leaf illustrating photosynthesis, with arrows showing sunlight, water, and carbon dioxide entering the leaf and sugars and oxygen being produced. A person is shown beside the tree to demonstrate the exchange of oxygen and carbon dioxide between plants and animals. — electromagnetic radiation Diagram of photosynthesis showing how water, light, and carbon dioxide are absorbed by a plant to produce oxygen, sugars, and more carbon dioxide.

Hot objects emit electromagnetic radiation across a range of frequencies because heat is the irregular, thermal motion of electrons, atoms, and molecules. As an object’s temperature increases, this motion becomes more rapid.1

Because electrons are significantly lighter than atoms, their irregular thermal motion creates irregular oscillatory charge motion. Each oscillation at a specific frequency acts like a tiny "antenna" that emits electromagnetic radiation. Because the thermal motion is irregular and involves a vast number of particles moving at varying speeds, the resulting radiation spans a continuous spectrum of frequencies rather than a single one.1

While the specific spectral distribution depends on the material, an ideal object known as a blackbody emits radiation across all frequencies based solely on its temperature. According to Planck’s radiation law, these emissions are quantized, meaning energy is released in discrete packets proportional to the frequency of the oscillation. As temperature rises, the peak intensity of this emitted radiation shifts toward higher frequencies.21