For many years, astronomers have believed that galaxies are not scattered randomly across space. Instead, they sit along an enormous invisible network of dark matter and gas called the cosmic web. Now, an international team has captured the clearest direct image of one of its threads.
Led by Davide Tornotti, a PhD student at the University of Milano-Bicocca in Italy, researchers photographed a faint hydrogen filament stretching three million light-years through space. At each end sits a galaxy with a supermassive black hole feeding on gas and shining as a quasar. The light from this filament has been travelling for almost 12 billion years.
When this light first started its journey, the Universe was only about 2 billion years old. Galaxies were growing rapidly, pulling cold gas from their surroundings to create stars. Cosmologists believe they did this by drawing material along filaments like the one Tornotti's team has now observed.
To capture the image, the team used MUSE, an advanced telescope at Cerro Paranal in Chile's Atacama Desert. The observation required extreme patience, with researchers watching a single area of sky for hundreds of hours. What they discovered was a thread of gas connecting two ancient galaxies, glowing because radiation from their quasars makes the hydrogen around them shine.
When the team compared their observations with computer simulations, the results matched perfectly. This is the first time astronomers have directly seen and photographed a cosmic filament with such clarity, confirming that the universe's hidden skeleton exists exactly as theory predicted.