Stars forming in clusters from a single galactic dust cloud are not as similar to one another as previously thought, according to an international team of astronomers who analysed ‘starquakes’ from just three months of data from NASA’s Kepler space telescope. And there is at least another four years’ data to come.
“In the past, it was assumed that the only difference [between stars in the same cluster] would be their mass,” says Dennis Stello of the University of Sydney. “But the seismology [data] tells us that might not be correct. There’s probably a spread in age or in composition because the original cloud of gas was not homogeneous.”
Launched in March 2009, the Kepler observatory monitors the brightness of some 145,000 stars in its field of view every half-hour. Among other things, this data can be used to measure starquakes, which can provide information on size, temperature and internal composition of stars.
Starquakes occur when hot gas boils to the surface and releases energy, thus cooling and sinking in the process. “The star becomes like a big gong in a sand storm,” says Dennis, who leads two groups of about 60 scientists working on cluster stars. “Every such convection event is like a sand grain hitting it. The whole star sets up many internal standing waves each vibrating at different frequencies.” This leads to slight changes in temperature at the surface, which in turn leads to the small changes in the luminosity or amount of light emitted—and that is what is detected by the Kepler telescope.