Lyman-Alpha blobs (for real, that’s what they’re called) are huge clouds of hydrogen gas, sometimes hundreds of thousands of light-years across. They glow at a wavelength that doesn’t make sense. We’ve been staring at the first such blob, called Lyman-Alpha blob 1 or LAB-1 for short, since we found it in 2000. Now a team of scientists from the UK, working with the ALMA interferometer and teamed up with scientists from the Hubble project and the Keck Observatory, have figured out why the blob glows like it does. It’s the primordial cloud from which a superlatively huge cluster of galaxies is forming — or was, 11.5 billion years ago.

The discovery hinges on the resolving power of the ALMA interferometer. Because the individual telescopes are so far apart, their effective diameter is equal to their separation on the ground. Pointing the interferometer at the blob let astronomers resolve it into multiple separate star nurseries within a swarm of young galaxies, all buried in the center of a huge cloud of gas.

Working with Hubble to do deep imaging and the Keck Observatory to do the spectroscopy, the team also found that these star nurseries are surrounded by numerous companion galaxies. The birth of galaxies is not a peaceful process, and these young galaxies could be bombarding the star nurseries with high-energy matter, driving star formation.

The scientists then used a sophisticated model of galaxy formation to show that the UV-band radiation LAB-1 throws off can be explained if ultraviolet light produced by those star nurseries gets scattered by the space blob — something like the backscatter you get using high beams in a rainstorm. This would explain why we see the blob lit from within.

As for why that light is at this weirdish wavelength, Lyman-alpha radiation is produced when electrons in hydrogen atoms fall back to their lowest energy level from one level up. The packet of energy lost is released as light with a wavelength, in this case falling in the UV band.

Redshifted enough, as is the case with the enormous distance between us and the space blob, UV light becomes visible to the human eye here on Earth. This let the team sanity-check their findings by comparing data from the ground-based ALMA interferometer with the Hubble space telescope.

Beyond being pleased to have finally got the space blob into sharp focus, the extended Lyman-alpha glow provides information on what goes on in the primordial gas clouds from which young galaxies form: a region that is very difficult to study, but critical to understand. From these observations, we can start to piece together a deep history of the visible universe. Between now and then, check out the deep zoom of the space blob: