Article from SAC in Nature: New measurements help understand an oscillating type of star

13. May 2020

A group of stars called delta Scuti are difficult to measure because their brightness fluctuates irregularly. Therefore, astrophysics has long been interested in the study of this mischievous type of star. Now, an international research team, led by researchers from the Center of Excellence SAC at the University of Aarhus, recently published a study in Nature after their discovery of regular fluctuations in the brightness of 60 delta Scuti stars. The new data help us to understand this mystical type of star and its role in the universe.

The image shows the bright delta Scuti star from which the type of stars examined by the international study draws its name.
The image shows the bright delta Scuti star from which the type of stars examined by the international study draws its name. Photo: ESO

In a clear and dark night sky during the summer, one can see the star delta Scuti shine brightly from the stellar constellation Scutum. This star has given its name to a whole class of stars that vary in brightness in such a way that they are significantly complex and hard for researchers to study.

But now an international research team, led by researchers from the DNRF center SAC at Aarhus University, has succeeded in studying 60 vibrating delta Scuti stars with observations from NASA’s space telescope TESS. The study, which was published in Nature today, is the first of its kind to discover regular fluctuations in the brightness of these stars, which are also called fluctuating or pulsating stars.

“Until now, there has been too much mess in the many mixed-up tones and rhythms we have seen to understand this type of pulsating star. It has been somewhat like listening to a cat walking across the keys of a piano. The extremely precise data from NASA’s satellite TESS made it possible for us to cut through the noise to have a structure that sounds more like nice piano chords,” said Professor Timothy Bedding, lead author behind the study and the director of the SAC group in Sydney.

Access to the interior of the star

In studying oscillating stars such as the delta Scuti stars, the researchers are usually looking for regular oscillations in the brightness of the stars. For this, they use observations from space telescopes such as NASA’s TESS, which can measure tiny variations in the brightness of thousands of stars at the same time, and over several weeks. While the oscillation pattern of a star like the sun will be calm and regular, the oscillation patterns of most delta Scuti stars will often be quite irregular. But now Professor Bedding and the rest of the international research team have discovered 60 of the thousands of delta Scuti stars that have been observed by TESS, all of which exhibit a regular oscillation pattern.

“The results here are amazing and very important, and with them, we can better understand the mechanisms that drive these vibrant stars. It’s something that has been hidden from us for 120 years – since the first delta Scuti star was discovered,” said Victoria Antoci, a co-author of the study and a scientist at SAC for eight years.

As part of the study, the researchers compared the regular pattern of the 60 delta Scuti stars with theoretical calculations, and with the method called asteroseismology, they were able to look into the interior of the stars through the variations observed by TESS on the surface of the stars. In this way, the researchers could gain an insight into processes in the stars’ interior that are otherwise inaccessible. The new study contributes to the researchers’ knowledge of the fundamental properties of stars – knowledge that can have a major impact on our understanding of both the stars and the universe at large.

“Now we can begin to study the inner conditions of these variable stars, and so we can learn even more about how stars work in detail and under specific conditions. We will become clearer about how our more well-behaved star, the sun, works and why it is so relatively stable and calm, and thus in our place in the universe, ” said Professor Jørgen Christensen-Dalsgaard, head of center at SAC. He added:

“For example, the new results could be used to determine the ages of groups of stars that appear in heaps and in star currents – stars that clump together and have not yet learned the rules of social distancing!” 

You can read the scientific article from SAC in Nature here

More information about the study can be found in a press release from SAC here