This image shows the new filament, which connects four galaxy clusters: two on one end, two on the other. These clusters are visible as bright spots at the bottom and top of the filament (four white dots encircled by colour). A mottled band of purple stretches between these bright dots, standing out brightly against the black surrounding sky; this is the filament of X-ray-emitting hot gas that had not been seen before, and contains a chunk of ‘missing’ matter. The purple band comprises data from Suzaku. The astronomers were able to identify and remove any possible ‘contaminating’ sources of X-rays from the filament using XMM-Newton, leaving behind a pure thread of ‘missing’ matter. These sources can be seen here as bright dots studded through – and removed from – the filament’s emission. Credit: ESA/ XMM-Newton and ISAS/ JAXA.
Astronomers using ESA’s XMM-Newton and JAXA’s Suzaku X-ray space telescopes believe they may have found long-theorised missing matter.
The astronomers have discovered a huge filament of hot gas bridging four galaxy clusters. At ten times as massive as our galaxy, the thread could contain some of the Universe’s ‘missing’ matter, addressing a decades-long mystery.
Over one-third of the ‘normal’ matter in the local Universe – the visible stuff making up stars, planets, galaxies, life – is missing. It hasn’t yet been seen, but it’s needed to make our models of the cosmos work properly.
These models suggest this elusive matter might exist in long strings of gas, or filaments, bridging the densest pockets of space.
While we’ve spotted filaments before, it’s tricky to make out their properties; they’re typically faint, making it difficult to isolate their light from that of any galaxies, black holes, and other objects lying nearby.
New research is now one ofthe first to do just this, finding and accurately characterising a single filament of hot gas stretching between four clusters of galaxies in the nearby Universe.
Lead researcher Konstantinos Migkas, of Leiden Observatory in the Netherlands, said: “For the first time, our results closely match what we see in our leading model of the cosmos – something that’s not happened before. It seems that the simulations were right all along.”
XMM-Newton on the case
Clocking in at over ten million degrees, the filament contains around ten times the mass of the Milky Way and connects four galaxy clusters: two on one end, two on the other.
All are part of the Shapley Supercluster, a collection of more than 8,000 galaxies that forms one of the most massive structures in the nearby Universe.
The filament stretches diagonally away from us through the supercluster for 23 million light-years, the equivalent of traversing the Milky Way end to end around 230 times.
Konstantinos and colleagues characterised the filament by combining X-ray observations from XMM-Newton and Suzaku, and digging into optical data from several others.
The two X-ray telescopes were ideal partners: Suzaku mapped the filament’s faint X-ray light over a wide region of space, while XMM-Newton pinpointed very precisely contaminating sources of X-rays – namely, supermassive black holes – lying within the filament.
Co-author Florian Pacaud of the University of Bonn, Germany, said: “Thanks to XMM-Newton we could identify and remove these cosmic contaminants, so we knew we were looking at the gas in the filament and nothing else.
“Our approach was really successful, and reveals that the filament is exactly as we’d expect from our best large-scale simulations of the Universe.”
A simulation of the ‘cosmic web’, the vast network of threads and filaments that extends throughout the Universe. Stars, galaxies, and galaxy clusters spring to life in the densest knots of this web, and remain connected by vast threads that stretch out for many millions of light-years. These threads are invisible to the eye, but can be uncovered by telescopes such as ESA’s XMM-Newto. Credit: Illustris Collaboration/ Illustris Simulation.
Not truly missing
As well as revealing a huge and previously unseen thread of matter running through the nearby cosmos, the finding shows how some of the densest and most extreme structures in the Universe – galaxy clusters – are connected over colossal distances.
It also sheds light on the very nature of the ‘cosmic web’, the vast, invisible cobweb of filaments that underpins the structure of everything we see around us.
Norbert Schartel, ESA XMM-Newton project scientist, said: “This research is a great example of collaboration between telescopes, and creates a new benchmark for how to spot the light coming from the faint filaments of the cosmic web.
“More fundamentally, it reinforces our standard model of the cosmos and validates decades of simulations: it seems that the ‘missing’ matter may truly be lurking in hard-to-see threads woven across the Universe.”
Piecing together an accurate picture of the cosmic web is the domain of ESA’s Euclid mission.
Launched in 2023, Euclid is exploring this web’s structure and history. The mission is also digging deep into the nature of dark matter and energy – neither of which have ever been observed, despite accounting for a whopping 95% of the Universe – and working with other dark Universe detectives to solve some of the biggest and longest-standing cosmic mysteries.
The study is published in Astronomy and Astrophysics.
