Dark matter will bend time

Weak gravitational lenses as a powerful tool for cosmologists: Researchers measure the distribution of matter in distant groups and clusters of galaxies

Light deflection shows distribution of matter

Berkeley (USA) - Distant groups and clusters of galaxies show the same relationship between the strength of their X-rays and their total mass as similar structures in our closer cosmic neighborhood. This is shown by the investigation of the deflection of light by the force of gravity in the galaxy clusters by an international team of researchers. These "weak gravitational lenses" are becoming an important tool for measuring the cosmos, write the astronomers in the "Astrophysical Journal".

So far, such measurements have been limited to nearby galaxy clusters. "We have now been able to expand them to smaller structures in an earlier time in the cosmos," explains Alexie Leauthaud from the Lawrence Berkeley National Laboratory, one of the participating scientists. "This improves our understanding of the relationship between the normal matter that we see through X-rays and the dark matter that we see through the deflection of light."

The gravity of groups and clusters of galaxies bends the rays of light from more distant objects on their way through the cluster of galaxies to Earth. This also changes the appearance of distant galaxies, they are deformed. Since the shape of the galaxies themselves is very different, this deformation due to the weak gravitational lens effect can only be determined by the statistical evaluation of a large number of background objects.

This is exactly what Leauthaud and her colleagues did on 206 galaxy clusters and groups. Detailed X-ray observations were available for each of these collections, which enabled the researchers to determine the center of mass. This is because the X-rays come from hot gas between the galaxies and show a clear concentration towards the center of mass of the galaxy cluster. From the measurement of the statistical deformation of the background galaxies, the astronomers were able to derive the distribution of the total mass and thus also of the dark matter.