This image of a
nebula in the constellation Aquila (the Eagle) shows that young stars are lighting up parts of the cloud. The protostars are tucked away in dark filaments.
In visible light all you would see is a dark nebula. But this picture is from the Herschel Space Observatory which observed in the infrared. The Hubble Space Telescope made some beautiful pictures of stellar nurseries, but it's only through the development of infrared telescopes and radio telescopes that people could really study them closely.