A computer illustration of a Lyman-alpha blob. The image has been coloured so that cold gas appears red and hot gas appears white. Red clumps in the image represent smaller galaxies surrounding two larger star-forming galaxies. Credit: J.Geach/D.Narayanan/R.Crain
Astronomers have discovered the nature of a massive object spotted in the distant Universe known as a Lyman-alpha Blob (LAB).
These objects are massive clouds of hydrogen that emit ultraviolet light, but the story behind their formation has remained a mystery, until now. Observations have revealed two galaxies at the heart of one LAB that are rapidly forming stars and giving off immense light.
A team of astronomers studied SSA22-Lyman-alpha blob1, one of the largest LABs known, and found two galaxies at its centre that are forming stars at a rate over 100 times that of the Milky Way.
Additional observations showed that the galaxies are surrounded by lots of smaller galaxies that may be firing material into them, feeding the frenzied star formation.
The team believe they are witnessing the formation of a massive galaxy cluster 11.5 billion lightyears away.
A computer simulation of galaxy formation showed how the giant glowing cloud could be explained as ultraviolet light produced by the galaxies’ star formation hitting the hydrogen gas surrounding it.
Lead author of the study Jim Geach says:
“Think of a streetlight on a foggy night - you see the diffuse glow because light is scattering off the tiny water droplets.
A similar thing is happening here, except the streetlight is an intensely star-forming galaxy and the fog is a huge cloud of intergalactic gas. The galaxies are illuminating their surroundings.”
Astronomers believe Lyman-alpha Blobs could be the places where the most massive galaxies in the Universe form.
If true, Lyman-alpha Blob 1 may be the site of formation of a massive elliptical galaxy that will eventually form the core of a galaxy cluster.