We have been looking at the sky for centuries and creating theories about how the universe holds itself together, but now finally someone has managed to capture a real image of a filament of the cosmic web. Yes, a giant and ghostly structure that connects galaxies and that, until now, we could only guess at with simulations, calculations and a lot of imagination. The image is dizzying and measures more than three million light years (a lot, if you cannot do the math).
The photo was taken after hundreds of hours of observation with the MUSE spectrograph of the VLT telescope in Chile and has left the scientific community amazed, no wonder. Seeing with your own eyes something that has been traveling through space for at least 12 billion years does not happen every day.
But… what is the cosmic web?
The universe is connected by a sort of spider web, they do not float, everything is a huge spider web made of gas and dark matter and it shapes and keeps the entire universe working.
At the intersections of those filaments, just like in the knots of a net, the brightest galaxies are born. And within that web, dark matter acts like a sort of magnet that concentrates gas and drags it. The problem is that, until now, it had not been possible to see it directly. We only knew it existed because the light from distant objects was deformed when passing through it, but now we do not have to imagine it anymore.
What exactly have they seen?
A team from the University of Milano-Bicocca together with scientists from the Max Planck Institute for Astrophysics (MPA) has been the first to clearly capture a filament that connects two active galaxies, both with supermassive black holes in the center. And they achieved it thanks to the use of MUSE (Multi-Unit Spectroscopic Explorer), a spectrograph installed at the European Southern Observatory in Chile.
The most incredible thing is that they managed to differentiate the gas that is part of those galaxies from the one that floats through intergalactic space. And that, for scientists, is like going from having a hand-drawn map to having a satellite photo.
And everything fits perfectly with the computer simulations that already existed. In other words, the theory we had about how the universe is structured on a large scale is beginning to be confirmed with real evidence.
The key role of the VLT telescope
Capturing something so distant and so faint is not like pointing a camera and done. To achieve it, they had to use the MUSE spectrograph as we told you before, this device can break down light into all its wavelengths and see what is invisible to the naked eye.
For days and days, the scientists focused on the same area of the sky until the signal appeared. And they knew it was the perfect moment.
Why this matters
Beyond how spectacular the image may seem, the important thing is what it means. Seeing directly the gas that connects two galaxies helps us better understand how they form, how they grow and what feeds them.
Every time we manage to detect another filament like this, we will be closer to understanding the complete puzzle of the universe, incredible!
And this has only just begun
This is just the first piece. There are already plans to continue looking for more filaments with the VLT and, in the future, with the Extremely Large Telescope (ELT), which will be even more powerful. The idea is to put together a detailed map of how matter flows through the universe. A sort of Google Maps of the cosmos.
“We are delighted with this direct and high-definition observation of a cosmic filament. But, as they say in Bavaria: ‘Eine ist keine’ (one does not count)” Fabrizio Arrigoni Battaia, Scientist at MPA.
Do you want to read the full study? Here it is!