This patch of blackness on the sky, known as Barnard 68, is a dark molecular cloud

This patch of blackness on the sky, known as Barnard 68, is a dark molecular cloud. Barnard 68 nebula appears so dark because the light from the stars is blocked. This happens because the atoms and molecules that exist in there are of the right physical size to absorb practically all the visible light emitted from background stars.

The surrounding darkness help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. The absence of stars at the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. Image credit: ESO

Learn more: https://www.eso.org/public/news/eso9934/