Alex McColgan

In this image, you can see what they found.

A filament of the cosmic web connecting four galaxy clusters, two on each end, each one as a white spot surrounded by colour.

The band of purple stretched between them, resembling a honeycomb, or bone marrow-like texture, is the filament of X-ray emitting hot gas.

Located in the Shapley Supercluster, a supercluster of more than 8000 galaxies, the filament stretches across a distance of 23 million light years, which is the equivalent of about 230 Milky Ways end to end.

Its mass comes in at roughly 10 times that of the entire Milky Way galaxy, and the temperature of the filament's hot gas is a scorching 10 million degrees Celsius.

It reveals in detail for the first time how galaxy clusters are connected over colossal distances, and uncovers the vast cosmic web that underpins the structure of our entire universe, like the very bones of a cosmic skeleton upon which everything else forms.

And according to the paper's co-author, the filament is exactly what we expected from the best large-scale cosmological simulations of the universe.

We got it right.

The latest breakthroughs in observing filaments lend important evidence and support for our current standard model of cosmic evolution, known as the Lambda Cold Dark Matter model.

The model is underpinned by dark matter, which has been too complicated for us to catch a glimpse of thus far, so observing this once-thought-missing visible matter on the cosmic web is a big step in the right direction.

But to truly know whether our models match reality, we need more than one or two filaments.

We need to map the entire skeleton, or at least much more of it.

And that is where another mission, Euclid, comes in.

Launched in 2023, Issa's Euclid mission is designed to piece together a more accurate picture of the cosmic web's structure and history, and dig into the nature of dark matter and dark energy.

Euclid will help us measure galactic shapes with precision, revealing how dark matter distorts space through gravitational lensing and measure redshifts, giving us a 3D position for each galaxy.

This combination will allow Euclid to infer the locations of the dark matter filaments, not just the galaxies on them, and give us precise locations to look for more gas.

By 2030, Euclid will likely be able to confirm if the cosmic web matches results from the XMM-Newton filament discovery, and the pattern seen in the cosmic microwave background

If it's a perfect match, that would be one of the strongest confirmations of the Big Bang model in the history of science.

If not, then something is fundamentally missing in our standard model, whether it's our understanding of dark matter, gravity, or the early universe.

Either way, with the help of Euclid and the latest observations of these cosmic filaments, cosmology is poised to be changed forever.