Why are newly forming protostars often detected as infrared objects?

Newly forming protostars are often detected as infrared objects because they are deeply embedded within dense, opaque molecular clouds composed of gas and dust.12

As a protostar undergoes gravitational collapse, it generates an intense radiation field that attempts to escape the surrounding envelope of material. The dust within this envelope is highly opaque to shorter-wavelength radiation, such as visible light, which is absorbed by the dust particles. This absorbed energy is then re-emitted by the dust at longer, infrared wavelengths. Consequently, the visible light produced by the protostar is degraded, and the object becomes apparent to distant observers primarily through its infrared radiation, which can flow around the dust particles and escape the cloud. This process explains why many candidate protostars, including those sometimes called "cocoon stars," are identified as infrared sources rather than visible ones.1342