While the Universe is a big place, and everything in it may seem thrown everywhere, there is quite a bit more structure than we can see.
According to our models of the Universe and its growing evidence, dark matter filaments connect massive objects such as galaxies and galaxy clusters into a vast cosmic network.
It is along these filaments that the hydrogen that feeds into the galaxies flows, but they are not so easy to see: among all the stars and galaxies and bright galactic nuclei, the faint emission of hydrogen diffuses into the galaxy. intergalactic space is hard to see, never mind map.
Still, we are one step closer. At the culmination of years of work, an international team of astronomers led by Roland Bacon of the Center for Astrophysical Research in Lyon, France, has just directly imagined several filaments of the cosmic network at the beginning of the Universe, in about 12 billion light-years away.
Hydrogen filaments (in blue). (Roland Bacon / David Mary / ESO / NASA)
Their results are not just some of the strongest tests of the cosmic network; they also found evidence that a large population of dwarf galaxies potentiates the glow of hydrogen within the filaments. This discovery could dramatically alter our understanding of the formation of galaxies in the childhood of the Universe.
Because the cosmic network is so hard to see, many of our tests so far have been indirect. Some scientists have used the way mass bends space-time (gravitational lensing) to look for distortions in the path of distant light, suggesting that a chain in the cosmic network lies 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)
At the top: Cosmological simulation of the distant universe, with light emitted by hydrogen atoms in the cosmic network in a region about 15 million light-years in diameter.
Bacon and his team took a different approach: they were contemplating a tiny little portion of the sky for a long time, with a really impressive telescope. Using the MUSE instrument on ESO’s Very Large Telescope in Chile, 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 had been conducted, with astronomers looking for filaments of light in a cluster of galaxies: gas wires ionized by the galaxies themselves. Here, too, Bacon’s team’s work differs from previous efforts: previous research investigated an extreme environment, while new research deliberately seemed somewhere indescribable.
After the planning phase, the team’s observations took months to obtain, from August 2018 to January 2019. They had to be taken in blocks during the New Moon to minimize interference.
(Thibault Garel / Roland Bacon)
At the top: 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).
The team then had to process and analyze the data, which took another year. But it was worth it, as 40% of the galaxies in their data were not detectable in the ultra-deep field, but researchers had imagined bright hydrogen in cosmic network filaments, spanning millions of light-years.
Fascinatingly, the team’s analysis shows that most of the hydrogen emission could be accounted for by a large population of star-forming dwarf galaxies, 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 enormous implications for our understanding of the Universe.
If dwarf galaxies are also being channeled along the filaments of the cosmic network, like drops of water down a piece of rope, it could help explain how galaxies formed and grew, and grew to prodigious sizes in the early universe, an issue that has baffled cosmologists.
In addition, searching for the emission of star-forming dwarf galaxies could help us find more filaments in the cosmic network and understand more deeply how the entire universe is connected.
The research has been published in Astronomy and astrophysics.