Simulated Spiral Galaxy (IMAGE) Center for Astrophysics | Harvard & Smithsonian Caption Powerful new computer simulations are allowing astronomers to understand how spiral arms in galaxies form and survive. These simulations suggest that the arms arise as a result of the influence of giant molecular clouds - star forming regions or nurseries common in galaxies. Introduced into the simulation, the clouds act as "perturbers" and are enough to not only initiate the formation of spiral arms but to sustain them indefinitely. In this frame from one such simulation, more than 100 million "stellar particles" form the familiar shape of a spiral galaxy. Credit Thiago Ize & Chris Johnson (Scientific Computing and Imaging Institute) Usage Restrictions None License Licensed 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.