Giant cosmic blob found lit from the inside

A brilliant blob of gas that sprawls more than 300,000 light-years across is illuminated from the inside, thanks to two galaxies furiously churning out stars.

Observations from a fleet of telescopes showed the “Lyman-alpha blob”, which is 11.5 billion light-years from Earth, contains the large pair along with a swarm of smaller galaxies which what appears to be the early phase in the formation of a massive galaxy cluster.

The work is published in Arxiv and will appear in the Astrophysical Journal.

Lyman-alpha blobs are gigantic clouds of cool hydrogen gas which give off a certain ultraviolet wavelength of light (called Lyman-alpha radiation).

The first Lyman-alpha blob was found in 2000 and called LAB-1. But why they’re so radiant has been a mystery.

So a team of astronomers, led by Jim Geach, from the University of Hertfordshire, UK, peered into LAB-1’s depth with the Atacama Large Millimetre/submillimetre Array in Chile, which can observe light from such cool dust clouds. 

Combining data with that from the Very Large Telescope, also in Chile, they mapped the Lyman-alpha light and found the galaxies within LAB-1 are forming stars at a rate of around 150 each year – more than 100 times faster than the Milky Way galaxy.

The Hubble Space Telescope and Keck Observatory picked out the smaller galaxies surrounding the massive pair. These fainter counterparts could well be supplying the fuel that’s driving the star-forming frenzy.

Simulations supported this idea.

“Think of a streetlight on a foggy night – you see the diffuse glow because light is scattering off the tiny water droplets,” Geach explains. 

“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.”