A density wave. (IMAGE) Ecole Polytechnique Fédérale de Lausanne Caption Illustration of a density wave. Made by Harald Ritsch. Credit Innsbruck University/EPFL. Usage Restrictions This content is distributed under a Creative Commons CC BY-SA 4.0 license. You may freely reproduce the text, videos and images it contains, provided that you indicate the author’s name and place no restrictions on the subsequent use of the content. If you would like to reproduce an illustration that does not contain the CC BY-SA notice, you must obtain approval from the author. 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.