The vast, virtually invisible network of fibers that stretch and connect the Universe have finally been discovered to glow in the dark. In the distant reaches of intergalactic space, astronomers have directly detected the faint glow of these filaments as they stretch across the abyss. Previously, our only findings of this vast network were observed around objects such as quasars, the brightest light sources in the Universe. Today we see it in the shadows, where much of the web lurks. “Before this latest discovery, we had seen filamentary structures comparable to street lights,” said Caltech astrophysicist Christopher Martin. “Now we can see them without lights.” Although there are vast distances stretching between objects in the Universe, it is not a series of isolated islands as first appearances might suggest. Our models of the Universe suggest that there is a vast cosmic web of dark matter, bands of which stretch across these distances, connecting galaxy to galaxy, cluster to cluster.

Although there are vast distances stretching between objects in the Universe, it is not a series of isolated islands as first appearances might suggest. Our models of the Universe suggest that there is a vast cosmic web of dark matter, bands of which stretch across these distances, connecting galaxy to galaxy, cluster to cluster. Along these filaments, which clustered under the influence of gravity in the early stages of the Universe, hydrogen from the sparse intergalactic medium would accumulate and flow away. This hydrogen is thought to fuel growing galaxies, providing them with new material to create sparkling stars. Narrowband image shows the filament detection location. (Martin et al., Nat. Astron., 2023) In a universe filled with shiny things, it’s not easy to detect the faint glow of cold, diffused hydrogen. But its discovery is an important goal in astronomy and cosmology. This could give us information about how the Universe continues to evolve and develop, as well as where the Universe’s invisible dark matter and missing regular matter may be hiding: an estimated 60 % of the hydrogen formed in the Big Bang will reside in the cosmic web. . “The cosmic web delineates the structure of our universe,” Martin explains. “This is where most of the normal or baryonic matter in our galaxy resides and directly maps the location of dark matter.”

So, to hunt down the most elusive parts of the cosmic web, Martin and his colleagues designed a specialized instrument to look for weak Lyman alpha emission – the spectral signature of hydrogen when it absorb and re-emit radiation. The Keck Cosmic Web Imager (KCWI) is located at the W. M. Keck Observatory on Maunakea, Hawaii. The universe has many different types of light, including solar system light and galactic light. When observed from Earth, this light is further complicated by atmospheric light. So Martin devised a way to remove this light from KCWI’s observations. frameborder=”0″allow=”accelerometer; Autorun; write to clipboard; encrypted media; gyroscope; picture in picture; web-share”allowfullscreen> “We’re looking at two different regions of the sky, A and B,” he explains. “The filament structures will be at different distances in both directions in the arrays, so you can take the background light from image B and subtract it from A, and vice versa, leaving only the structures . I ran detailed simulations on this in 2019 .. to convince myself that this method would work.

“The filament structures will be at different distances in both directions in the arrays, so you can take the background light from image B and subtract it from A, and vice versa, leaving only the structures . I ran detailed simulations on this in 2019 .. to convince myself that this method would work. Next, the researchers studied areas of the sky, looking for concentrations of Lyman alpha lines. Because the Universe is expanding, wavelengths of light at greater distances attenuate toward the red end of the spectrum; therefore, the redder the emission, the farther away the light is. This allowed the team to map the emission in three dimensions – light travels between 10 and 12 billion years to reach us. This represents a time in the history of the Universe when everything was still in its early stages of formation, after the Big Bang 13.8 billion years ago. The result is the first glimpse of the complex cosmic web in the darkest corners of the Universe. Researchers say this offers a new way to monitor the cosmic web, track the Universe’s matter and find out how it all comes together.

source: https://www.nature.com/articles/s41550-023-02054-1