Molecular Clouds (3) ...

Prior studies have had to rely on using radio telescopes to detect trace molecules such as carbon monoxide or ammonia in cold molecular clouds and then using this information to determine indirectly the distribution of molecular hydrogen. Advances in infrared (IR) detection give now for the first time a way to peer directly into the center of such stellar birthplaces, as illustrated in the following images.

Dark Cloud Barnard 68
The adjacent European Southern Observatory image shows a molecular cloud called Barnard 68 in the constellation Ophiuchus (the Serpent Holder). It is about 500 light years away and about a half light year in diameter. A high concentration of molecular hydrogen and dust causes the molecular cloud to absorb all light from the stars behind it. The centers of such molecular clouds are probably among the coldest places in the Universe. The formation of many stars begins by condensation of regions within such molecular clouds.
Studying Molecular Clouds at Long Wavelengths
The following image shows the molecular cloud Barnard 68 at six different wavelengths. The wavelength 0.44 micrometers corresponds to blue light, 0.55 micrometers to yellow-green, and the longer wavelengths to the near IR portion of the spectrum. Clearly the longer wavelength IR light penetrates the cloud much better than visible light. This illustrates an important property of interstellar light extinction by dust: the amount of extinction is strongly wavelength dependent. In particular, we see that IR observations are much less prone to distortion by absorption in intervening dust.