Hubble image of MACS J0717 with mass overlay. (Photo : NASA/Hubble)
You can't see it. You can't feel it. But if current theories are correct, dark matter makes up well more than half the mass in our known universe. Scientists are keen on trying to understand this mysterious form of matter, and in the attempt, have studied a filament of dark matter in 3D for the first time.
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To create a 3D image of the 60-million-light-year-long dark matter filament, the scientists combined a series of images taken from telescopes such as NASA's Hubble Telescope, and NAOJ's Subaru Telescope.
Dark matter is thought to be the main cause of the clustering of galaxies. Filaments of dark matter are thought to extend from galaxy cluster to galaxy cluster creating a web-like network of support that determines the spatial positioning and structure of our universe due to its mass and gravitational pull on matter.
"Filaments of the cosmic web are hugely extended and very diffuse, which makes them extremely difficult to detect, let alone study in 3D," says Mathilde Jauzac lead author of the study.
The study required four key steps.
First was identifying a suitable area to study.
"From our earlier work on MACS J0717, we knew that this cluster is actively growing, and thus a prime target for a detailed study of the cosmic web," explains co-author Harald Ebeling.
Next up was actually seeing the filament. Since dark matter is invisible, it can only be observed by the gravitational effect that it has on the objects around it - and in the vastness of space, light is sometimes the only thing present. So in order to correctly spot the filament, the scientists had to use advanced gravitational lensing techniques.
Third was creating high-enough resolution images to actually be able to study the dark matter filament. This is where the number of telescopes came in. Combining and utilizing different views gave the astronomers a more complete picture.
The last ingredient thrown in the melting pot were numerical measurements of distances and motions. After a few stirs, the computer was then able to generate a 3D model, which should help reveal more about the mysterious, universal force known as dark matter.