New deep observations of the early universe have led to an unexpected discovery: some very distant quasars are surrounded by large halos of cool gas. This finding brings into question several assumptions astronomers had about how galaxies form and evolve.

Quasars are incredibly active galaxies, where the supermassive black hole is eating up material so quickly that the energy released outshines the rest of the galaxy. In previous surveys, only 10 percent of quasars were shown to have a halo but in this new sample, 100 percent of them do.

The research, available online and to be published in the Astrophysical Journal, focused on 19 quasars between 11.5 and 12.1 billion light-years away, and looked at the properties of their halos. Typically they extend from 350,000 to over 1 million light-years from the quasar and have a temperature of about 10,000 kelvins.

“It is still too early to say if this is due to our new observational technique or if there is something peculiar about the quasars in our sample. So there is still a lot to learn; we are just at the beginning of a new era of discoveries”, says lead author Elena Borisova, from the ETH Zurich, in a statement.

The presence of this cold gas is unaccounted for in our current picture of galaxy evolution. Ten thousand kelvins is very hot for human standards but significantly cooler than expected when we consider the intergalactic medium (IGM). The IGM is usually extremely hot, with temperatures of millions of degrees, and very low densities (less than an atom per cubic meter).

The study was possible thanks to a new instrument called MUSE (Multi Unit Spectroscopic Explorer) installed on the Very Large Telescope in Chile. The instrument let astronomers produce observations of extended objects where every pixel of the image has a full spectrum of light.

“We have exploited the unique capabilities of MUSE in this study, which will pave the way for future surveys. Combined with a new generation of theoretical and numerical models, this approach will continue to provide a new window on cosmic structure formation and galaxy evolution,” co-author Sebastiano Cantalupo added.

The team hopes that future surveys will expand on this analysis, studying a larger number of quasars and also studying these 19 objects in more detail.