What is the definitive evidence confirming the presence of a luminous, deeply embedded protostar?

Answer

Strong infrared (IR) emission

During the protostar phase, the central mass accumulates significant material, causing gravitational potential energy to convert into thermal energy, leading to intense heating. However, this heat is initially trapped by the thick cocoon of surrounding dust and gas, rendering the object invisible in optical wavelengths—hence the term 'deeply embedded.' The definitive observational evidence shifts from radio/millimeter observations used for cold gas to infrared astronomy. The surrounding dust envelope absorbs the energy radiated by the central object and subsequently re-radiates this energy at longer wavelengths. Therefore, detecting strong emission in the mid- to far-infrared spectrum confirms that there is a luminous, hot source hidden within the opaque cloud, serving as the hallmark signature of a true protostar.

What is the definitive evidence confirming the presence of a luminous, deeply embedded protostar?

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