Watch the pulsations of a Delta Scuti star! In this illustration, the star changes in brightness when internal sound waves at different frequencies cause parts of the star to expand and contract. In one pattern, the whole star expands and contracts, while in a second, opposite hemispheres swell and shrink out of sync. In reality, a single star exhibits many pulsation patterns that can tell astronomers about its age, composition and internal structure. The exact light variations astronomers observe also depend on how the star's spin axis angles toward us. Delta Scuti stars spin so rapidly they flatten into ovals, which jumbles these signals and makes them harder to decode. Now, thanks to NASA's Transiting Exoplanet Survey Satellite, astronomers are deciphering some of them.
Astronomers have detected elusive pulsation patterns in dozens of young, rapidly rotating stars thanks to data from NASA's Transiting Exoplanet Survey Satellite (TESS). The discovery will revolutionize scientists' ability to study details like the ages, sizes and compositions of these stars — all members of a class named for the prototype, the bright star Delta Scuti.
Geologists studying seismic waves from earthquakes figured out Earth's internal structure from the way the reverberations changed speed and direction as they traveled through it. Astronomers apply the same principle to study the interiors of stars through their pulsations, a field called asteroseismology.
Sound waves travel through a star's interior at speeds that change with depth, and they all combine into pulsation patterns at the star's surface. Astronomers can detect these patterns as tiny fluctuations in brightness and use them to determine the star's age, temperature, composition, internal structures and other properties.
But scientists have had trouble interpreting Delta Scuti pulsations. These stars generally rotate once or twice a day, at least a dozen times faster than the Sun. The rapid rotation flattens the stars at the poles and jumbles the pulsation patterns, making them more complicated and difficult to decipher.
Using new data from TESS and archived information from ground observatories and NASA's now-retired Kepler space telescope, astrophysicists identified a batch of 60 Delta Scuti stars with clear patterns for the first time.
Sound waves bouncing around inside a star cause it to expand and contract, which results in detectable brightness changes. This animation depicts one type of Delta Scuti pulsation — called a radial mode — that is driven by waves (blue arrows) traveling between the star's core and surface. In reality, a star may pulsate in many different modes, creating complicated patterns that enable scientists to learn about its interior.
Hear the rapid beat of HD 31901, a Delta Scuti star in the southern constellation Lepus. The sound is the result of 55 pulsation patterns TESS observed over 27 days sped up by 54,000 times. Delta Scuti stars have long been known for their apparently random pulsations, but TESS data show that some, like HD 31901, have more orderly patterns
Credit: NASA's Goddard Space Flight Center and Simon Murphy, University of Sydney
This visualization shows pulsations of the Delta Scuti variable star HD 31901, based on brightness measurements by NASA's Transiting Exoplanet Survey Satellite (TESS). The movie compresses 24 hours of TESS data into 33 seconds, a speed increase of nearly 2,700 times.