A team of astronomers has found new evidence that red giant stars suffer from ‘defects’ (extreme structural differences) in their inner cores, reports RT. hydrogen inside
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 reconstructed the internal structure of more than 350 stars by studying their oscillation patterns . . It can be seen on their roofs.
The researchers used data from NASA’s Kepler space telescope and a technique called “seismology” to probe the cores of ancient stars, much like seismologists use earthquakes to probe our planet’s interior.
Red giants are large, bright stars with a mass of about 0.3 to 8 times that of the Sun, which have reached the final 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 finally sets in—and the outward pressure of the melt eases—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 dramatically, up to hundreds of times their former size. As a result, the star’s surface becomes cold and red, leading to the name of these objects.
Since red giants are used in many scientific studies, as astronomical probes of distance, to help measure the densities of galaxies and to study the chemical evolution of stars, it is important to be able to correctly model their internal structure.
Although direct observation of the interior of the red giant is not possible, its internal structure can be inferred by measuring fluctuations in the surface of stars as a result of the frequencies and paths of sound waves passing through stellar bodies. .
Stars have different modes of oscillation that are sensitive to different parts of their interiors, and seismologists can use these models to explore different aspects of a star’s structure.
‘Wave propagation within stars leads to subtle differences in the brightness of stars that can be detected with high-resolution space instruments,’ explains Dr Margarida Kuna, astronomer at the Institute of Astrophysics and Space Sciences. that they emit, i.e. the physical properties inside the star.
In this study, Dr Kuna and colleagues looked at 359 red giants below a certain threshold mass and measured different properties, including different wobble frequencies, for each star.
The lead author, Dr.
He added that it provides for the first time the possibility of a detailed investigation of the physical processes occurring in this region. of these structures.
The analysis showed that about 7% of the stars studied showed structural discontinuities, so-called “defects” in their inner cores.
According to the scientists, two hypotheses have been proposed to explain how this defect works. The first shows that they were present during stellar evolution, but are usually too faint to be classified as true nebulae. The team says this scenario is not supported by the results of their study.
The second hypothesis proposes that the defect is “switched off” by an unknown physical process which subsequently leads to changes in the structure of the star’s inner core.
However, more detailed data is needed before scientists can give weight to 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.’
