A hidden cosmic web revealed in the young universe

Section of the Line Intensity Map created by charting the distribution and concentration of excited hydrogen (via the Lyman alpha wavelength) in the universe ten billion years ago. The stars mark where HETDEX has found galaxies. The inset simulates the structure present in this map once it is zoomed in on and background noise is removed from the data. Credit: Maja Lujan Niemeyer/Max Planck Institute for Astrophysics/HETDEX, Chris Byrohl/Stanford University/HETDEX.

doi.org/10.3847/1538-4357/ae3a98
Credibility: 989
#Universe

Astronomers have managed to map, for the first time in great detail, a vast invisible structure formed by faint galaxies and gas clouds in the primordial universe

This hidden cosmic web existed between 9 and 11 billion years ago, at a time when the universe was only about 2.5 to 4.5 billion years old.

Until now, scientists could mainly observe the brightest and most active galaxies from that distant phase, which emit intense light due to the accelerated formation of stars.

However, most of the smaller galaxies and diffuse gas clouds remained invisible because their light is too faint.

Using data from the HETDEX project, carried out with the Hobby-Eberly Telescope, the team applied a technique called line intensity mapping.

Instead of hunting galaxies one by one, they measured the collective brightness of Lyman-alpha light-emitted by energized hydrogen-over large areas of the sky.

It’s like looking at a city from above at night: traditional methods only show illuminated metropolises, while this approach also captures the diffuse light of neighborhoods, villages, and roads, revealing the whole picture.

The survey analyzed an immense amount of information-hundreds of millions of spectra collected in a region equivalent to more than 2,000 full moons in the sky.

Although HETDEX was primarily designed to study dark energy through the brightest galaxies, the researchers used the remaining data (about 95%) to detect this subtle glow.

With the help of supercomputers, they created a three-dimensional map that highlights both the regions around known galaxies and the spaces between them, previously considered practically empty.

Example of a spectrum created by statistically combining the spectra of 50,000 Lyman alpha emitters from the first Public HETDEX Source Catalog. The wavelength associated with Lyman alpha appears as a dramatic peak, making it a particularly useful tool for identifying the location of bright galaxies in the early universe. Credit: HETDEX

The result shows a web-like structure far richer and more complex than previously imagined, with filaments of matter connecting small galaxies and gas clouds.

This discovery offers a much more complete view of how galaxies formed and evolved in the first billion years of the universe, and allows us to test whether current computer simulations accurately describe the physics of that time.

Scientists now intend to cross-reference this map with other surveys that observe different elements, such as carbon monoxide, to better understand the environments where stars were born.

This work marks the beginning of a new phase of cosmic exploration, using techniques that reveal what was previously hidden, and opens doors to even more precise future observations.

Published in 03/15/2026 00h21

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Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.

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