As our telescopes improve, we can look further back into our universe's past to determine where the galaxies we see today came from. Sometimes, though, we find something that doesn’t really match with our theories. Today is one of those times.

An international team of researchers has announced the discovery of a gigantic hydrogen nebula located 10 billion light-years away. This seems to be an enormous Lyman-alpha nebula (ELAN), a rare group of gigantic gas clouds that shine thanks to the enormous energy of quasars. But this one, called MAMMOTH-1, doesn’t appear to have a quasar inside.

The study, which was accepted for publication in the Astrophysical Journal and is available online, is part of the MApping the Most Massive Overdensities Through Hydrogen (MAMMOTH – hence the object name). The same team previously discovered another ELAN called the “Slug Nebula”, which unlike MAMMOTH-1 hosts a quasar.

"It's extremely bright, and it's probably larger than the Slug Nebula, but there's nothing else visible except the faint smudge of a galaxy. So it's a terrifically energetic phenomenon without an obvious power source," senior author J. Xavier Prochaska, a professor from UC Santa Cruz, said in a statement. “I expect there's a quasar that is so obscured by dust that most of its light is hidden."

According to the standard cosmological model, galaxies are distributed in filaments made of dark matter. This structure, known as the cosmic web, formed quickly after the Big Bang around 13.8 billion years ago.

"From the distribution of galaxies we can infer where the filaments of the cosmic web are, and the nebula is perfectly aligned with that structure," lead author Zheng Cai, also from UC Santa Cruz, added.

MAMMOTH-1 not only looks like a junction in the local cosmic web, but it appears to be a major one. It has an unusually high concentration of protogalaxies in an area just 50 million light-years across. If we could observe it today, it would be an incredibly packed galaxy cluster only 1 million light-years across.

MAMMOTH-1 is a nice tease of what we are yet to discover. When observatories like the James Webb Space Telescope come online, they will look further back into the universe, and these now peculiar objects will likely be part of common sights from the dawn of time.

^{Surface brightness map of MAMMOTH-1 Cai et al., Astrophysical Journal}