Lyman-alpha Blob

A bubble Lyman-alpha (Lyman-alpha blob - LAB), is a huge cloud of hydrogen, an enormous concentration of gas the size of several galaxies, ie, a size of several hundred thousand light-years.
The LAB are the largest known objects in the Universe. Some of these soft structures are more than 400 000 light years in diameter.
These gigantic structures of hydrogen, the beginnings of the universe, like a nebula, they emit strongly in emission line Lyman-alpha hydrogen.
Normally, the Lyman-alpha emission is in the ultraviolet, but the bubbles Lyman-alpha are so distant that their light is red-shifted, and become visible in the optical domain.
Data from the X-ray observations indicate the presence of a supermassive black hole, feeding in an active galaxy, itself located inside the bubble primitive.
The bubbles Lyman-alpha could represent an early stage of the formation of galaxies and their black holes. Lyman-alpha bubbles hold valuable clues for scientists to determine how galaxies formed.
The most famous bubble Lyman-alpha was discovered in 2000 by Steidel and Matsuda.
Since, using the Subaru Telescope National Astronomical Observatory of Japan, over 30 LAB, smaller (200 million light years), were found.
Is not known at present, neither the mechanism that produces the emission line Lyman-alpha, or how the LAB are connected to the surrounding galaxies.

"We showed for the first time the influence of this enigmatic object is from the light scattered by the luminous galaxies that are hidden rather than the brightness own gas spread throughout the cloud," said Matthew Hayes (University of Toulouse , France), in the article by the journal Nature on August 18, 2011: "Central Powering of the Largest Lyman-alpha Nebula is Revealed by Polarized Radiation” by Hayes et al.

Image: Bubble Lyman-alpha, a mosaic of images taken in X-ray, optical and infrared both from space and from Earth. This bubble Lyman-alpha is seen in the past, where it was when the Universe was only 2 billion years, there are about 12 billion years.
Credit: NASA / ESA, CXC, JPL-Caltech, STScI, NAOJ, J.E. Geach (Univ. Durham) et al.

NB: In astronomical spectroscopy, Lyman-alpha forest is the sum of absorption lines arising from the Lyman-alpha transition of neutral hydrogen in the spectra of distant galaxies and quasars.