Lyman-alpha blob

So far they have only been found in the high-redshift universe because of the ultraviolet nature of the Lyman-alpha emission line.

The most famous Lyman-alpha blobs were discovered in 2000 by Steidel et al.[1] Matsuda et al., using the Subaru Telescope of the National Astronomical Observatory of Japan extended the search for LABs[2] and found over 30 new LABs in the original field of Steidel et al.,[1] although they were all smaller than the originals.

These LABs form a structure which is more than 200 million light-years in extent.

It is currently unknown whether LABs trace overdensities of galaxies in the high-redshift universe (as high redshift radio galaxies—which also have extended Lyman-alpha halos—do, for example), nor which mechanism produces the Lyman-alpha emission line, or how the LABs are connected to the surrounding galaxies.

Lyman-alpha blobs may hold valuable clues to determine how galaxies are formed.

Animation of a Lyman-alpha blob.
The giant Lyman-alpha blob LAB-1 (left) and an artist's impression of what it might look like if viewed from relatively close (right).
Composite of two different images taken with the FORS instrument on the Very Large Telescope of the Lyman-alpha blob LAB-1 in the constellation of Aquarius . Credit ESO /M. Hayes.