on beat

Astronomers listen to the pulsating rhythm of a mysterious class of stars

Jumbled up notes turned into smooth piano.

NASA's Goddard Space Flight Center

For decades, astronomers have listened to the stars' beating hearts. The stellar music is not only cosmically soothing, but it also provides scientists with crucial data on the internal structure of stars, as well as their mass and age.

However, one class of stars, known as delta Scuti, has been a little off beat, creating music that scientists could not seem to understand. That's until a group of delta Scuti stars was discovered producing a harmonious tune.

A team of researchers used data from NASA's Transiting Exoplanet Survey Satellite (TESS) to detect the pulsation patterns of delta Scuti stars by listening to the sounds of a group of 60 young, rapidly rotating stars.

The study, published Wednesday in the journal Nature, is a breakthrough in scientists' ability to identify the characteristics of this elusive class of stars.

"It was a mess, like listening to a cat walking on a piano."

"Previously we were finding too many jumbled up notes to understand these pulsating stars properly," Tim Bedding a professor of astronomy at the University of Sydney, and lead author of the new study, said in a statement. "It was a mess, like listening to a cat walking on a piano."

Delta Scuti are a medium sized, pulsating class of stars that are 1.5 to 2.5 times the mass of the Sun. They are named after a star that was first detected in 1900, shinning bright in the constellation Scutum.

Scientists have discovered thousands of these variable stars, but they can be difficult to understand. The stars' pulsation did not produce a clear pattern, which is frustating, but that's because delta Scuti stars rotate a dozen times faster than the Sun, doing a full rotation once or twice a day, which causes their poles to flatten and that in turn jumbles up their pulsation patterns.

However, using the TESS data, the team of scientists behind the new study identified a group of 60 delta Scuti stars creating a regular, high-frequency pulsation pattern.

"The incredibly precise data from NASA's TESS mission have allowed us to cut through the noise," Bedding said. "Now we can detect structure, more like listening to nice chords being played on the piano."

The team behind the new study believe that this group of 60 stars is younger than other delta Scuti stars observed before. As the stars age, their pulsation slows down and other signals interfere with its patterns.

What kind of music do stars create? In order to take a closer look at the insides of a star, astronomers observe their pulsations. Stellar pulsations are sort of a star's breath, with its outer layers expanding and contracting so that the star could maintain its equilibrium.

When those pulsations take place, the star varies in brightness. Sound waves travel through the interior of the star at speeds that vary with depth, and they combine into pulsation patterns at the surface of the star, according to NASA.

Astronomers listen to these patterns, and it helps them find out the star's different properties such as its age, temperature, composition and internal structure. This branch of science is called asteroseismology, and it helps astronomers not only study distant stars in the cosmos, but get a better understanding of our own host star and its sometimes erratic behavior.

By using the data obtained by the new study, scientists were already able to identify the age of a delta Scuti star dubbed HD 3190 by creating an asteroseismic model of the star. They determine that HD 31901 is a mere 120 million years old.

The audio file reveals the cosmic rhythm of the pulsating star, and settles a long standing debate about its age.

"Delta Scuti stars have been frustrating targets because of their complicated oscillations, so this is a very exciting discovery," Sarbani Basu, a professor of astronomy at Yale University in New Haven, Connecticut, who was not involved in the study, said in a statement. "Being able to find simple patterns and identify the modes of oscillation is game changing. Since this subset of stars allows normal seismic analyses, we will finally be able to characterize them properly."

Abstract: Asteroseismology probes the internal structures of stars by using their natural pulsation frequencies1. It relies on identifying sequences of pulsation modes that can be compared with theoretical models, which has been done successfully for many classes of pulsators, including low-mass solar-type stars2, red giants3, high-mass stars4 and white dwarfs5. However, a large group of pulsating stars of intermediate mass—the so-called δ Scuti stars—have rich pulsation spectra for which systematic mode identification has not hitherto been possible6,7. This arises because only a seemingly random subset of possible modes are excited and because rapid rotation tends to spoil regular patterns8,9,10. Here we report the detection of remarkably regular sequences of high-frequency pulsation modes in 60 intermediate-mass main-sequence stars, which enables definitive mode identification. The space motions of some of these stars indicate that they are members of known associations of young stars, as confirmed by modelling of their pulsation spectra.
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