Threads of the universe: Cosmic web revealed in unprecedented detail

Matter in intergalactic space is not randomly scattered – it forms a vast network of filamentary structures that make up the cosmic web. These filaments, composed of gas and dark matter, serve as the backbone on which galaxies develop and evolve. 

Now, an international team of researchers has obtained the sharpest image to date of one such filament.

This cosmic web spans three million light-years and connects two actively forming galaxies from when the universe was only about two billion years old.

The study was conducted by researchers at the University of Milano-Bicocca and the Max Planck Institute for Astrophysics (MPA). 

Tracing the shape of a cosmic web

The team used the Multi-Unit Spectroscopic Explorer (MUSE) instrument on the Very Large Telescope (VLT) at the European Southern Observatory (ESO) in Chile. 

The findings provide direct insight into how intergalactic gas flows through cosmic webs to fuel star formation in galaxies.

“By capturing the faint light emitted by this filament, which traveled for just under 12 billion years to reach Earth, we were able to precisely characterize its shape,” explained Davide Tornotti, a Ph.D. student at the University of Milano-Bicocca. 

“For the first time, we could trace the boundary between the gas residing in galaxies and the material contained within the cosmic web, through direct measurements.”

Challenge of detecting intergalactic gas 

A cornerstone of modern cosmology is the concept that dark matter constitutes about 85% of all matter in the universe. Gravity causes dark matter to arrange itself into a complex network of filaments, with the brightest galaxies forming at their intersections. 

These filaments act as conduits, channeling gas to feed star formation. Yet, directly imaging the gas within these structures has long been a formidable challenge due to its extremely faint emission.

Traditional methods of detecting intergalactic gas have relied on observing its absorption of light from distant, bright background sources. 

Even hydrogen, the most plentiful element, emits only a weak glow, making it nearly impossible to capture with earlier instruments.

Most detailed view of a cosmic web 

To overcome these obstacles, Tornotti and his colleagues embarked on one of the most ambitious observation campaigns ever attempted with MUSE. 

The team dedicated hundreds of hours to one region of the sky, which enabled them them to capture an ultrasensitive image of a cosmic filament at high significance. The resulting image is the most detailed view ever obtained of such a structure, and directly reveals how gas bridges the gap between galaxies.

“When compared to the novel high-definition image of the cosmic web, we find substantial agreement between current theory and observations,” noted Tornotti.

The detailed data allowed the team to delineate the filament’s structure and provided direct measurements of its shape, which gave new information concerning the constraints on the gas properties within these intergalactic bridges.

Simulations confirm observations

In addition to direct imaging, the researchers used advanced supercomputer simulations from the MPA to model the expected emissions from cosmic filaments, based on current cosmological theories. 

When the simulated predictions were compared with the high-definition image obtained from MUSE, the results showed significant agreement. 

This alignment between simulation and observation is crucial, as it reinforces our understanding of how gas is distributed and flows in the cosmic web.

Paving the way for future discoveries

The study of this filament marks a significant step forward in our ability to directly observe the structures that feed galaxy formation.

“We are thrilled by this direct, high-definition observation of a cosmic filament,” said Fabrizio Arrigoni Battaia, an MPA staff scientist involved in the study. 

“But as people say in Bavaria: ‘Eine ist keine’ – one doesn’t count. So we are gathering further data to uncover more such structures, with the ultimate goal of having a comprehensive vision of how gas is distributed and flows in the cosmic web.”

Future observations with MUSE, combined with additional data from upcoming astronomical surveys, promise to unveil more such filaments. 

These efforts will ultimately help scientists map out the detailed distribution of gas in the cosmic web and refine models of how galaxies are fueled and evolve over cosmic time.

Secrets of galaxy formation

By directly imaging this cosmic filament, researchers have opened a new window into the fundamental processes that govern galaxy formation and evolution. 

This breakthrough not only confirms key aspects of our cosmological models but also demonstrates the power of modern astronomical instruments in revealing the delicate structure of the universe. 

As more data becomes available, scientists hope to further constrain the physical properties of intergalactic gas, which would lead to a deeper understanding of the intricate web that connects all galaxies across the cosmos.

The study is published in the journal Nature Astronomy.

Image Credit: Alejandro Benitez-Llambay/Universität Mailand-Bicocca/MPA

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