What are cocoon stars and why are they hidden from visible-light telescopes?

In astronomy, "cocoon stars" are newly formed, massive stars that remain completely enshrouded within the dense, chaotic clouds of gas and dust from which they were born.12

These stars are hidden from visible-light telescopes because the surrounding dust is highly opaque to shorter-wavelength radiation. While visible light is easily absorbed and scattered by these dust grains, infrared radiation—which is generated as the dust is heated by the young star—can pass through the cloud relatively unimpeded. Consequently, these stars are undetectable in the optical spectrum but can be observed as intense infrared sources using specialized infrared telescopes.134