Astronomers discover regular rhythms in mysterious pulsating stars

Using NASA's planet-hunting telescope, astronomers nail down the rhythm of delta Scuti stars.

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Jackson Ryan
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A screenshot of a simulation showing the pulsations of star HD 31901

Chris Boshuizen/Simon Murphy/Tim Bedding

The stars speak! Understanding stars, including our own sun, has largely revolved around examining their outsides: the surfaces and surrounding atmospheres we can see. Although we can't look inside a star, we can listen to the rumbling it makes based on pulsations and oscillations that occur in the interior. Studying the pulses, astronomers are able to decipher what's happening in the heart of a star.

For a particular class of stars, known as delta Scuti stars, it has been difficult to nail down the rhythm. But now, thanks to NASA's latest planet-hunting space telescope, astronomers have pulled back the insanely hot curtain on this class of stars to get a sense of what happens inside. 

A new study, published in the journal Nature on Wednesday, details the rhythm of dozens of delta Scuti stars, which are about two times as massive as our sun, finding they exhibit clear, obvious rhythms. The discovery provides a new way for astronomers to understand the unusual physics occurring within the hearts of these stars, which are relatively common across the galaxy.

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To tune into the insides of the stars, astronomers at the University of Sydney turned to NASA's Transiting Exoplanet Survey Satellite, which has been performing an extensive survey of the cosmos since its launch in 2018. The satellite is designed to hunt for planets around other stars by dividing the sky into sectors and taking snapshots of all the blazing furnaces in its field of view. Every two minutes, TESS grabs a quick image of the sky and measures the brightness of thousands of stars to determine how that changes over time. A dip in brightness might correspond to a planet passing in front of the star.

But the research team wasn't looking for distant planets. Instead, it used the extremely precise changes in brightness detected by TESS to look at the stars themselves.The incredibly tiny changes in brightness correspond to pulsations and oscillations in the heart of the star. Because TESS can resolve the brightness of stars so exquisitely, it creates a great data set for trying to listen to a star's heartbeat. 

The team focused in on a batch of TESS data containing a sample of 92,000 stars and, with some clever coding, was able to develop a tool to quickly sift through the huge data set. A chance finding in the TESS data led to a list of around 1,000 stars with similar rhythms. Eventually, the researchers were able to nail down the list to 57 delta Scuti stars with discernible rhythms.

The stars are all relatively close to us, in galactic terms, lying between 60 and 1,400 light-years away. For reference, the Milky Way Galaxy is over 100,000 light-years wide. 

Tim Bedding, an astronomer at the University of Sydney and first author on the paper, said the new data allowed his team to "cut through the noise."

"Previously we were finding too many jumbled up notes to understand these pulsating stars properly," he said in a release. "It was a mess, like listening to a cat walking on a piano." Using the TESS data, things became a lot clearer. Bedding says now it's more like "listening to nice chords being played."

The rhythms of many other types of stars have been discovered in the last few decades, including those of huge, red giants like Betelgeuse, which has allowed astronomers to determine what's happening inside the blazing hot balls of gas. Although delta Scuti stars are widely distributed across the universe, previous research had failed to find a regular rhythm. 

"We think this is because they rotate rapidly, which makes the patterns less regular," said Bedding.  

With a pattern of pulses now understood, future research will be able to more accurately determine the age of stars and help astronomers pick apart how galaxies and star systems might evolve. 

"We are now in a position to start to probe these stars, and to use them as benchmarks to help us interpret the huge numbers of other stars in the group that present more complicated pulsation spectra," said Bill Chaplin, an astronomer at the University of Birmingham and co-author on the study. 

NASA's TESS is still surveying the sky and sending mountains of data back to Earth each month. Bedding says it's sometimes likened to "drinking from a fire hose," and there are many more sectors to look through. His team will now examine other, more complex delta Scuti stars to see if they can identify patterns. 

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