Gostaria de saber o que é esta mancha tipo nuvem que aparece na imagem.

A referida mancha na imagem pretende representar a projeção do disco da nossa Galáxia. Para mais detalhes ver a resposta à pergunta 152. I would like to know what this kind of cloud-like blob on this image is. This blob is supposed to represent the projection of our galaxy's disk. For more details, check Question 152, "What is the location of the Milky Way in the known Universe? Where can I find pictures of the Universe that are not directed towards the center, but outwards instead?".