Nature looks inside pulsing stars – not pulsars, but a group called “δ Scuti stars” – that flicker in a regular enough pattern that astronomers can use the frequency of the flickering to tell what they’re like *inside*:
But the light that reaches us originates from their upper layers — we can’t see inside. There is, however, a tool we can use to look into the interior of the stars: asteroseismology. Writing in Nature, Bedding et al. report that a subgroup of the enigmatic δ Scuti stars exhibits regular pulsations that will finally enable the stars to be probed using this tool.
Inside a star, gravity and gas pressure compete with each other. If the two are in balance, the star is in equilibrium, but if one increases more than the other, the star contracts or expands. Hot gas spheres such as stars can show characteristic periodic oscillations in which the star pulsates in this way. These characteristic oscillations, called eigenmodes, are standing waves, like the standing sound waves responsible for the sounds of musical instruments such as violins and oboes. The eigenmodes are determined by the physics of the oscillating system.
Space missions (such as CoRoT, Kepler and TESS) delivered the real breakthrough. Thanks to the missions’ long, homogeneous and evenly sampled light curves, and the precision of the collected data, asteroseismology has now been successfully applied to thousands of stars across several stellar types that have different internal structures
But the abundant star type known as δ Scuti, named after a star in the constellation Scutum, has remained one of the exceptions. Stars of this type have a slightly larger mass than that of our Sun, but their inner structure is very different. They have long been known to have complicated, low-amplitude light curves7. One might think that the large number of detected frequencies would make these stars ideal targets for asteroseismology.
Bedding et al. have identified a special subgroup of δ Scuti stars that pulsate at higher frequencies than do most such stars. For this subgroup, both theory and observations suggest the existence of regular frequency structures.
The authors show that these are young stars, which means that they can be used as tracers to estimate the age of open star clusters or of young stellar associations in our Galaxy. In this way, we might learn more about the evolution of the Milky Way.
Nature also included an audiovisual rendering of a δ Scuti star named HD 31901, as done by scientist and musician Dr. Chris Boshuizen.