Astronomers Discover Regular “Heartbeats” In Young Variable Stars

Animation of a delta scuti star pulsating. Dr Chris Boshuizen with assistance from Dr Simon Murphy and Prof. Tim Bedding 

There is a class of young pulsating stars known as delta Scuti variables. Slightly more massive than the Sun, because they are variables, their brightness fluctuates, pulsating in a matter of hours. Astronomers have previously detected many pulsations in these stars but were challenged by the fact these variations changed from star to star, and didn't appear to have a pattern. For this reason, this class has so far defied a complete understanding. At least, until now.

An international team of researchers detected what they call high-frequency pulsation modes in 60 delta Scuti stars between 60 to 1,400 light-years away and found that they were regular. Their study, published in Nature, was able to make sense of the complex rhythm of these ever-changing stars.

“Previously we were finding too many jumbled up notes to understand these pulsating stars properly,” lead author Professor Tim Bedding from the University of Sydney said in a statement. “It was a mess, like listening to a cat walking on a piano.”

The team studied almost 100,000 light-curves – graphs that show the brightness of an object over a period of time – from stars collected by NASA’s Transiting Exoplanet Survey Satellite (TESS). The state-of-the-art spacecraft can record star variations for a large number of stars. By studying the variations recorded over a long period, the team was able to spot the elusive patterns, or "heartbeat" of the stars, allowing them to peer into the heart of these perplexing stars.  

“The incredibly precise data from NASA’s TESS mission have allowed us to cut through the noise. Now we can detect structure, more like listening to nice chords being played on the piano,” said Professor Bedding. “This definitive identification of pulsation modes opens up a new way by which we can determine the masses, ages, and internal structures of these stars.”


It is not just the availability of data that allowed this discovery, it's also how the data is processed. Star are complicated beasts, and in the case of variable stars, the changes in brightness we measure are affected both by how the internal pulsations happen and also how it is recorded by our instruments. Stars rotate after all, so that has to be taken into account. 

“We needed to process all 92,000 light curves, which measure a star’s brightness over time. From here we had to cut through the noise, leaving us with the clear patterns of the 60 stars identified in the study,” explained co-author Daniel Hey, a PhD student at the University of Sydney and co-author of the paper, who designed the software that allowed the team to process the TESS data.

The paper also confirms that some of these stars hang around together in so-called loose associations, and were likely to have formed altogether. “Our results show that this class of stars is very young and some tend to hang around in loose associations," Professor Bedding said. "They haven’t got the idea of ‘social distancing’ rules yet.” 

The identification of regular pulses in these stars can help researchers better estimate their internal structure, mass, and age, which will, by extension, allow us to estimate the age of other stars as well.

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