In the study, published in the journal Nature Communications and conducted by a team of astronomers led by the Institute of Astrophysics and Space Sciences (IA) in Lisbon, Portugal, scientists collected the internal structure of more than 350 stars by studying the oscillation patterns seen on their surfaces.
The researchers used data from NASA’s Kepler space telescope and a technique known as “seismology” to delve into the cores of ancient stars, much like seismologists use earthquakes to explore our planet’s interior.
Red giants are large, bright stars with a mass of about 0.3-8 times the mass of the Sun, which have reached an advanced stage of stellar evolution. Stars like the Sun release energy by converting hydrogen to helium through nuclear fusion, but the supply of hydrogen to the inner core is limited
And when that starts to run out — and the outward pressure of the melt decreases — they collapse under their own gravity. At this point, the star’s temperature increases until it reaches the point where hydrogen fusion can begin, but this time in a shell around the star’s inner core.
The energy released in this process causes the star’s outer layers to expand exponentially to hundreds of times their former size. As a result, the surface of the star cools and turns red, which is what gives these objects their name.
Since red giants are used in many scientific studies, as astronomical distance probes, to help measure galactic density and study the chemical evolution of stars, it is important to be able to model them and their internal structures correctly.
While it is not possible to see the interior of the red giant directly, it is possible to deduce its internal structure by measuring the oscillations that appear on the surface of stars as a result of the frequencies and paths of sound waves passing through stellar bodies.
Stars have many different modes of oscillation that are sensitive to different parts of their interiors, and seismologists can use these models to explore different aspects of stellar structure.
“Waves propagating inside stars lead to subtle differences in stellar brightness that can be detected using high-resolution space instruments,” explains astronomer from the Institute of Astrophysics and Space Sciences, Dr Margarida Cunha. that propagate, i.e. the physical properties of the stellar interior.” .
In the study, Dr Cunha and her colleagues studied 359 red giants below a certain threshold mass, measuring several properties including different wobble frequencies for each star.
“This work provides the first characterization of structural discontinuities found in the cores of red giant stars,” said lead author, astronomer Dr.
He added that this allows “for the first time, to carry out an accurate investigation of the physical processes that occur in this region. By analyzing these differences, we can obtain not only the overall parameters of the star, but also information on the exact structure of these structures”.
The analysis revealed that around 7% of the stars studied showed structural discontinuities, so-called “glitches” within their inner cores.
According to the scientists, two hypotheses have been put forward to explain how this defect works. The first suggests that they exist during the evolution of stars, but are usually too faint to be classified as disruptions. The team says this scenario is not supported by the results of their study.
The second hypothesis proposes that this defect is “smoothed out” by an unknown physical process which subsequently leads to changes in the structure of the star’s inner core.
However, more accurate data will be needed before scientists can back up this idea. As astronomer Diego Pausini of the Institute of Astrophysics and Space Sciences explains: ‘This study shows the limitations of our models and gives us the opportunity to find a way to improve them.’