An international team of astronomers has observed the light from 15 million galaxies in an effort to uncover the properties of dark matter, one of the biggest mysteries of the universe.
Using the European Southern Observatory's (ESO) Very Large Telescope (VLT), the researchers scanned about 450 square degrees of the sky (slightly over 1 percent) to make the most accurate measurements of cosmic shear, tiny distortions in the light of galaxies due to the gravity of dark matter.
The observations are part of the Kilo Degree Survey (KiDS) and they appear to indicate that dark matter doesn’t clump up but remains smooth, stretching from galaxy to galaxy across the universe in what’s known as the cosmic web. The results are published in the Monthly Notices of the Royal Astronomical Society.
“This latest result indicates that dark matter in the cosmic web, which accounts for about one-quarter of the content of the Universe, is less clumpy than we previously believed,” co-author Massimo Viola of the Leiden Observatory in the Netherlands said in a statement.
The result will help refine how dark matter is modeled. Dark matter is “dark” because it doesn’t interact with light, only with gravity. And even the gravitational interaction is not that strong. You can’t have a dark matter planet, and the KiDS result indicates that dark matter is even smoother than previously thought.
This smoothness is actually lower than what was estimated from the observations by the European Space Agency’s Planck satellite. The new result is a substantial discrepancy, but it is definitely not a fatal blow for dark matter. Dark matter is still the best explanation for what we see in the universe, although we might not have nailed down all its properties yet.
“We see an intriguing discrepancy with Planck cosmology at the moment," added Konrad Kuijken, the principal investigator of the KiDS survey. "Future missions such as the Euclid satellite and the Large Synoptic Survey Telescope will allow us to repeat these measurements and better understand what the Universe is really telling us."
Measuring cosmic shear won’t be relegated to just observations though, as already supercomputers and researchers are preparing software to discover what dark matter really is.