What type of radiation dominates the early emission from a protostar, making it invisible to standard optical telescopes?

Answer

Far-infrared and millimeter wavelengths

Because the initial temperatures of the condensing object are very low (around 10 Kelvin), the energy radiated away peaks in the longer, cooler wavelengths of the far-infrared and millimeter spectrum, requiring specialized telescopes for detection.

What type of radiation dominates the early emission from a protostar, making it invisible to standard optical telescopes?
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