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Which wavelengths can astronomers use to observe ultracompact H II regions?

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H II region Centre of the Orion Nebula (M42). Astronomers have identified some 700 young stars in this 2.5-light-year-wide area. They have also detected over 150 protoplanetary disks, or proplyds, which are believed to be embryonic solar systems that will eventually form planets. These stars and proplyds generate most of the nebula's light. This picture is a mosaic combining 45 images taken by the Hubble Space Telescope.

Astronomers observe ultracompact H II regions using radio and far-infrared radiation wavelengths.1

These specific wavelengths are utilized because they are capable of penetrating the thick dust found within the molecular clouds where these young, dense nebulae are located. While the radio radiation is produced by the ionized gas itself, the far-infrared radiation is emitted by the surrounding dust that has been warmed by the luminosity of the embedded star.1