Lyman-alpha blob 1

Polarized image of LAB-1, shown as the faint, green gas cloud.

Lyman-alpha blob 1 (LAB-1) is a giant cosmic cloud of gas located at the southern constellation of Aquarius, some 11.5 billion light-years from Earth with a redshift (z) of 3.09. It was discovered unexpectedly in 2000 by Charles Steidel and colleagues, who were suveying for high-redshift galaxies using the 200 inch (5.08 m) Palomar telescope.

Left: Lyman alpha blob-1 as seen in Lyman-alpha (yellow), infrared (red) and ultraviolet (blue). The round blue object at the upper left of the blob is a giant galaxy. Right: Artist's impression of how the blob may look like if viewed from relatively close.

LAB-1 is the first discovered, and is the prototype of the class of objects called Lyman-alpha blobs—huge concentrations of gases emitting the Lyman-alpha emission line of hydrogen. It is also the largest of its kind, measuring 300,000 light years across, four times larger than the Milky Way. The blob appears green on the image because of the combination of the high redshift (z = 3) and the ultraviolet nature of the blob. Imaging with the European Southern Observatory's Very Large Telescope showed that much of the light from the blob is polarized, the proportion increasing and peaking at around 20% at a radius of 45 kiloparsecs (145000 light-years), forming a huge ring around the blob.

It is still unclear as to why this object is emitting the Lyman-alpha emission radiation. It is thought that the light is coming from galaxies within the central region of the blob. Light of such intensities could be from active galaxies or supermassive black holes actively absorbing matter.