Studying dark matter in distant galaxies (IMAGE) Scuola Internazionale Superiore di Studi Avanzati Caption At the centre of spiral galaxies – those near to us but also those billions of light-years away – there is a vast spherical region made up of dark matter particles. This region has two defining characteristics: a density that is constant out to a certain radius that amazingly expands over time, while the density decreases. Credit Gauri Sharma Usage Restrictions The use of this image is allowed only if directly linked to this research License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.