Although the Universe is a big place and all the things in it may seem to have been thrown all over the higgledy-piggledy, there is quite a lot of structure than we can see.
According to our models of the Universe and growing evidence, filaments of dark matter connect massive objects such as galaxies and groups of galaxies in a vast cosmic network.
Along these filaments, hydrogen flows, feeding into galaxies, but they are not so easy to see – among all the bright stars and galaxies and galactic nuclei, the low emission of diffuse hydrogen from intergalactic space is hard to see, never the map mind.
However, I took a step closer. Over the years, an international team of astronomers led by Roland Bacon of the Center for Astrophysical Research in Lyon, France, has just imagined directly several filaments of the cosmic network in the early universe, about 12 billion light-years away.
Hydrogen filaments (in blue). (Roland Bacon / David Mary / ESO / NASA)
Their results are not only some of the strongest evidence so far for the cosmic network; they also found evidence that a large population of dwarf galaxies fuels the glow of hydrogen in filaments. This discovery could dramatically change our understanding of the formation of galaxies in the childhood of the Universe.
Because the cosmic network is so hard to see, much of our evidence so far has been indirect. Some scientists have used the way the mass bends space-time – gravitational lenses – to look for warp in the path of distant light, suggesting that a thread of the cosmic network is between its source and us.
Other researchers use light from quasars, extremely bright distant galaxies, to look for light absorbed by hydrogen along the filaments.
(Jeremy Blaizot / SPHINX project)
Above: Cosmological simulation of the distant Universe, with light emitted by hydrogen atoms in the cosmic network in a region of about 15 million light-years.
Bacon and his team took a different approach – looking at a small part of the sky for a very long time, with a really wonderful telescope. Using the MUSE instrument on Chile’s very large ESO telescope, the team made an incredible 140 hours of observations of a section of sky that also appeared in the ultra-deep field of the Hubble Space Telescope.
Similar research has been done, with astronomers looking for light wires in a group of galaxies – ionized gas wires from the galaxies themselves. Here, too, the work of Bacon’s team differs from previous efforts: previous research investigated an extreme environment, while new research deliberately seemed somewhere undescribed.
After the planning stage, the team’s observations took months until they were obtained, from August 2018 to January 2019. These had to be taken in blocks during the new month to minimize interference.
(Thibault Garel / Roland Bacon)
Above: Cosmological simulation of a filament made up of hundreds of thousands of small galaxies (as seen in situ on the left, as seen by MUSE on the right).
Then, the team had to process and analyze the data, which lasted another year. But it was worth it – not only were 40% of the galaxies in their data undetectable in the Ultra Deep Field, but researchers imagined bright hydrogen in the filaments of the cosmic network, which stretch for millions of light-years.
Fascinatingly, the team’s analysis shows that most of the hydrogen emissions could be explained by a large population of dwarf galaxies that form stars, scattered along the filament. Of course, we cannot see them individually – they are too far away to solve them – but future work could help confirm this discovery, with huge implications for understanding the Universe.
If dwarf galaxies are also channeled along cosmic filaments, such as water droplets on a piece of string, it could help explain how galaxies formed and grew – and grew to prodigious dimensions in the early universe, a question that puzzled cosmologists.
In addition, searching for emissions of dwarf galaxies that form stars could help us find more filaments of the cosmic network and a deeper understanding of how everything is connected in the Universe.
The research was published in Astronomy and astrophysics.