A cosmic filament, 3 million light-years long, has been directly imaged for the first time — offering a new glimpse into the hidden framework of the Universe!
Matter in intergalactic space is arranged in a vast network of interconnected filaments, known as the cosmic web. Now, after hundreds of hours of observations, an international team of researchers has captured the sharpest-ever image of one of these cosmic filaments. This filament links two actively forming galaxies and dates back to a time when the Universe was only about 2 billion years old.
The Cosmic Web and Dark Matter
Dark matter, which makes up about 85% of all matter in the Universe, plays a crucial role in shaping cosmic structures. Under gravity’s influence, it forms a vast, intricate web of filaments. At the intersections of these filaments, the brightest galaxies take shape. This cosmic web serves as the backbone of the Universe, guiding the flow of gas that fuels star formation in galaxies. Studying how this gas moves and interacts could significantly improve our understanding of how galaxies form and evolve.
However, directly observing this intergalactic gas is extremely difficult. Scientists have mainly detected it indirectly — by measuring how it absorbs light from distant, bright objects. These observations, though valuable, do not clearly reveal how the gas is distributed. Even hydrogen, the most abundant element in the Universe, emits only a very faint glow, making it nearly impossible for previous-generation telescopes to detect this elusive gas.
A Breakthrough with MUSE and the Very Large Telescope
In this new study, an international team led by researchers at the University of Milano-Bicocca and including scientists at the Max Planck Institute for Astrophysics (MPA) obtained an unprecedented high-definition image of a cosmic filament using MUSE (Multi-Unit Spectroscopic Explorer), an innovative spectrograph installed on the Very Large Telescope at the European Southern Observatory in Chile.
Even with the advanced capabilities of this sophisticated instrument, the research group had to carry out one of the most ambitious MUSE observation campaigns ever completed in a single region of the sky, acquiring data over hundreds of hours to detect the filament at high significance.
The Sharpest Image Ever of a Cosmic Filament
The study, led by Davide Tornotti, PhD student at the University of Milano-Bicocca, used this ultrasensitive data to produce the sharpest image ever obtained of a cosmic filament spanning 3 million light-years and connecting two galaxies, each hosting an active supermassive black hole. The discovery, recently published in Nature Astronomy opens new avenues to directly constrain gas properties within intergalactic filaments and to refine our understanding of galaxy formation and evolution.
Tracing the Cosmic Web with Supercomputer Simulations
“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, explains Davide Tornotti. “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.” The researchers took advantage of supercomputer simulations of the Universe run at MPA to calculate predictions of the expected filamentary emission given the current cosmological model. “When comparing to the novel high-definition image of the cosmic web, we find substantial agreement between current theory and observations,” Tornotti adds.
What This Means for Our Understanding of the Universe
This discovery and the encouraging agreement with supercomputer simulations are key to understanding the tenuous gas environment around galaxies and open up novel possibilities to pin down the galaxies’ fuel supply.
Fabrizio Arrigoni Battaia, MPA staff scientist involved in the study, concludes: “We are thrilled by this direct, high-definition observation of a cosmic filament. 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 to have a comprehensive vision of how gas is distributed and flows in the cosmic web.”
Reference: “High-definition imaging of a filamentary connection between a close quasar pair at z = 3” by Davide Tornotti, Michele Fumagalli, Matteo Fossati, Alejandro Benitez-Llambay, David Izquierdo-Villalba, Andrea Travascio, Fabrizio Arrigoni Battaia, Sebastiano Cantalupo, Alexander Beckett, Silvia Bonoli, Pratika Dayal, Valentina D’Odorico, Rajeshwari Dutta, Elisabeta Lusso, Celine Peroux, Marc Rafelski, Mitchell Revalski, Daniele Spinoso and Mark Swinbank, 29 January 2025, Nature Astronomy.
DOI: 10.1038/s41550-024-02463-w
