Alex McColgan

And in 2023, scientists made a breakthrough.

At the WM Keck Observatory in Hawaii, a team of astronomers had designed a dedicated instrument to search for filaments of hydrogen, more specifically, DIMM.

Lyman alpha emission, the spectral fingerprint of hydrogen as it absorbs and re-emits radiation.

And it worked.

In fact, they've made entire 3D maps of these filaments.

This was just the start of the discoveries.

In January 2025, the picture sharpened dramatically.

A team of international astronomers captured one of the clearest direct images yet.

Using the Multi-Unit Spectroscopic Explorer, or MUSE, mounted on the Very Large Telescope at the European Southern Observatory, they imaged a pair of quasar host galaxies with a cosmic filament about 3 million light years long.

And using supercomputer models built on the MUSE data, researchers were able to simulate a filament that matches the one they observed in real life.

This was a spectacular achievement.

But there was a catch.

These observations were from the early universe.

They traced cooler hydrogen gas billions of years in the past, not hot, diffused material thought to contain most of the universe's missing baryonic matter today.

Our models predict it stretched along thin filaments of the cosmic web in the local universe, but here the signal is far fainter and harder to isolate.

We were stuck.

In June 2025, astronomers finally found what they were looking for.

They were able to isolate and spectroscopically measure the hot, low-density gas of an individual cosmic web filament in the local universe, marking a breakthrough moment in our quest to locate the missing baryonic matter.

A team of European researchers headed by lead author Konstantinos Migas at Leiden University in the Netherlands used JAXA's Suzaku X-ray Space Telescope to map a single filament in faint X-ray emissions over a wide area of space.

They then used the XMM-Newton to pinpoint sources of X-ray contamination, in this case supermassive black holes, which had to be removed from the data in order to map the filament.