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Astronomers make invisible dark matter visible

An international team of astronomers, including Professor Koen Kuijken, has published a series of online articles presenting the first results of a major search for dark matter. Never before have researchers been able to chart so precisely the characteristics of groups of galaxies and their dark matter. The results will appear in different journals over the coming period.

Kilo-Degree Survey

Left: a part of the heavens showing a cluster of galaxies. Right: the same part of the heavens, but with the invisible dark matter appearing as a pink cloud. Credit: Tudorica for the Kilo-Degree Survey Collaboration.
Left: a part of the heavens showing a cluster of galaxies. Right: the same part of the heavens, but with the invisible dark matter appearing as a pink cloud. Credit: Tudorica for the Kilo-Degree Survey Collaboration.

The international research project is known by the name ‘Kilo-Degree Survey’. The astronomers use the VLT Survey Telescope of the European Southern Observatory in Cerro Paranal in Chile. The panoramic camera, OmegaCAM, was developed under Dutch management. It was made specially to photograph large sections of the heavens in sharp detail so that dark material can be mapped.

What is it?

Dark matter is material that should be there according to calculations made by cosmologists, but that we can’t actually see. The astronomers looked at how light from distant galaxies curves around large clouds of dark matter en route to the Earth, and were able to develop a method that makes it possible to see the dark matter. Most galaxies, including our own Milky Way, exist in groups. Gravity makes them cluster together. The scientists believe that dark matter plays an important role in this process.

30 x more dark than visible matter

The first observations from the Kilo-Degree Survey show that the galaxies studied contain thirty times more dark matter than visible matter. Massimo Viola (Leiden University) is the lead author of one of the first publications: ‘We have also learned that the clearest galaxy is almost always in the centre of a mass of dark matter. This is in line with the theory that predicts that galaxies are pulled towards one another and that they clump together in the centre, although this had never been so observed so clearly before.’

2 million galaxies

The international team of researchers analysed the images of more than two million galaxies at a distance of some 5.5 billion light years from the Earth. The first results that are now being published are just the start. They come from the first 7% of the total area that will be chartedl. The research is a stepping stone to more fundamental measurements on the distribution of dark matter in space and the role of the still mysterious phenomenon of dark energy.

10 years of research

Professor Koen Kuijken has been working towards these initial results for more than ten years. From building the camera via planning the observations through to organising the data processing: ‘The technique we use, weak gravitational lensing, is a subtle effect. You can only make measurements by making large but also sharp images of the heavens. The VLT Survey Telescope was designed to do that.’

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