Illustris Composite (image) Harvard-Smithsonian Center for Astrophysics Caption This composite image from the Illustris simulation is centered on the most massive galaxy cluster existing today. It morphs from concentrations of dark matter (at left in blue and purple) to normal matter made mostly of hydrogen and helium gas (at right in red, orange and yellow). Credit Illustris Collaboration Usage Restrictions None 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.