On January 30, 2025, researchers from the University of Milano-Bicocca unveiled the first high-definition images of a cosmic filament that links two galaxies in formation, dating back to when the Universe was only 2 billion years old. This breakthrough was made possible through a study utilizing the Multi-Unit Spectroscopic Explorer (MUSE), an advanced spectrograph located at the Very Large Telescope of the European Southern Observatory in Chile.
The findings, published in Nature Astronomy, reveal a cosmic structure that offers new insights into dark matter. The research team, led by professors Michele Fumagalli and Matteo Fossati, conducted an extensive observational campaign with MUSE, gathering data over hundreds of hours.
Dark matter, constituting approximately 90% of all matter in the Universe, plays a crucial role in the formation and evolution of cosmic structures. Fumagalli noted that dark matter forms an intricate cosmic web of filaments where the brightest galaxies are located at their intersections. This web serves as a framework for the visible structures in the Universe, with gas flowing within the filaments to facilitate star formation.
For years, observing this cosmic web was challenging due to the faint glow emitted by the diffuse gas in these filaments, which was indistinguishable with previous instruments. MUSE's high sensitivity to light allowed scientists to capture detailed images of the cosmic web.
The study, led by doctoral student Davide Tornotti, produced the sharpest image yet of a cosmic filament stretching 3 million light-years across two galaxies, each hosting a supermassive black hole. Tornotti explained that by capturing the faint light from this filament, which traveled nearly 12 billion years to reach Earth, they accurately characterized its shape and delineated the boundary between the gas in the galaxies and the material in the cosmic web.
Additionally, the team conducted simulations of the Universe using supercomputers, comparing current cosmological model predictions with new data, finding substantial agreement between theory and observation. This research was supported by the Cariplo Foundation and the Ministry of University and Research through the Project Departments of Excellence 2023-2027 (BiCoQ, Bicocca Centre for Quantitative Cosmology).