For many years astronomers have known that the atmospheres of pulsating stars either expand or contract over time, but they have long puzzled over the question: “What physical mechanism drives these amazing dynamics?” Alex Lobel and Andrea Dupree of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge and Ronald Gilliland of the Space Telescope Institute discovered while looking at the star Betelgeuse that sometimes gas is expelled from one side of the star while it splashes down at the other, causing Betelgeuse to “beat” like a human heart. “We found the upper atmosphere or chromosphere warmer than the region below it and we observed that it also contracted and expanded during this period,” said Lobel, an astrophysicist at the CfA. “But, most surprisingly, a scan in fall 1998 suggests streams of gas that are heading in opposite directions — with velocities of about 10,000 miles per hour.”