為何一塊熱固體或一團熱氣體，在高壓力下會呈現連續的光譜?

In fact, any substance at a temperature can emit continuous spectrum. A substance glows when the frequency peak of the emitted spectrum falls within the visible range.

Gas under high pressure glows on its own because under high pressure, molecules are close apart and collide with each other at high speed. This frequent collision causes excitation of molecules, which resulted in the emission of electromagentic radiation.