The distribution of dark matter has been mapped in 3D for the first time, revealing how the mysterious substance has evolved over the lifetime of the universe. The results confirm that dark matter provided the scaffolding that allowed ordinary matter to clump together to form galaxies and clusters of galaxies. Dark matter is an invisible substance that betrays its presence through the gravitational tug it exerts on ordinary matter. It is six times more abundant than ordinary matter and is thought to have seeded the first distinct structures in the universe, which began as a very uniform soup of matter. Computer simulations suggest that the formation of dark matter clumps attracted surrounding gas, which then condensed to form galaxies and galaxy clusters. But this dark matter clumping process had never been confirmed observationally. Now, astronomers have mapped the changing distribution of both dark matter and ordinary matter over time. Nick Scoville, of Caltech in Pasadena, US, led the Cosmic Evolution Survey (COSMOS), which combined data from the world’s leading observatories to produce the map. The key to determining the dark matter distribution is an effect called gravitational lensing, by which light rays from a distant object such as a galaxy are bent by the gravity of an intervening concentration of matter. Although dark matter cannot be seen directly, its presence can be inferred by the way its gravity distorts the images of galaxies behind it. The Hubble Space Telescope (HST) mapped out these distortions over a patch of sky equivalent to the width of four Full Moons in the largest survey it has ever performed. It devoted 10% of its time over two years to complete the survey. The Subaru telescope on Mauna Kea, Hawaii, and the Very Large Telescope in Paranal, Chile, measured the spectrum of light from galaxies seen by Hubble, which allowed the galaxies‘ distances to be calculated. The XMM-Newton X-ray satellite contributed by mapping gas within galaxies and galaxy clusters – the most abundant form of ordinary matter in those objects.
These results were presented on Sunday at a meeting of the American Astronomical Society in Seattle, Washington, US.
COSMOS

Hubble Maps the Cosmic Web of „Clumpy“ Dark Matter in 3-D

First 3D map of the Universe’s dark matter scaffolding