Most astronomers gaze at the heavens and see stars. William Chaplin hears an orchestra — a celestial symphony in which the smallest stars are flutes, the medium-sized ones are trombones and the giants are reverberating tubas.
The sounds are internal vibrations that reveal themselves as a subtle, rhythmic brightening and dimming of a star, explains Chaplin, an astrophysicist at the University of Birmingham, UK, and a specialist in astroseismology. These waves provide information that astronomers can’t get in any other way: triggered by the turbulent rise and fall of hot gases on the star’s surface, the vibrations penetrate deep into the stellar interior and become resonating tones that reveal the star’s size, composition and mass (see ‘Celestial music’). So by watching for the characteristic fluctuations in brightness, says Chaplin, “we can literally build up a picture of what the inside of a star looks like”.
Better still, he adds, asteroseismologists are now hauling in the data wholesale. After years of being hampered by Earth’s turbulent atmosphere, which obscures the view of the Universe and has limited asteroseismology to about 20 of the brightest nearby stars, researchers have been astonished by the trove of information coming from a new generation of space observatories. Thanks to the French-led Convection, Rotation and Planetary Transits (COROT) space telescope, launched in 2006, and NASA’s Kepler space telescope, launched in 2009, they can now listen in on hundreds of stars at a time.
“We are in a golden age for the study of stellar structure and evolution,” says Hans Kjeldsen, an astronomer at Aarhus University in Denmark.