The New Calculation Of The Solar Spectrum Has Solved The Controversial Problem About The Composition Of Our Stars In The Past Decade

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Although our sun is much closer than any other star in the universe, it still has its mysteries. After all, it is 93million miles (150million kilometers) from the earth, and we have only a narrow view. In addition, its surface is hot -- its atmosphere is hotter, and it constantly ejects particles at a speed of about 1million miles per hour. No wonder we humans still have new discoveries.

In fact, astronomers have just solved a decade long solar abundance crisis: the conflict between the internal structure of the sun determined from solar oscillation (solar Optics) and the structure derived from the basic theory of stellar evolution, which in turn relies on the measurement of the chemical composition of the sun today. The new calculation of solar atmospheric physics has produced the latest results of different chemical element abundances, thus solving this conflict. It is worth noting that the sun contains more oxygen, silicon and neon than previously thought. The method adopted also ensures a more accurate estimation of the chemical composition of ordinary stars.

What do you do when a tried and tested method of determining the chemical composition of the sun seems to contradict an innovative and accurate technique for mapping the internal structure of the sun? This is the situation faced by astronomers who study the sun. Now, the new calculation results published by Ekaterina MAG, Maria Bergemann and their colleagues have solved this obvious contradiction.

The tried and tested method in this regard is spectral analysis. To determine the chemical composition of the sun or any other star, astronomers often turn to spectroscopy: splitting light into iridescents of different wavelengths. The stellar spectrum contains obvious and sharp dark lines, which were first noticed by William Wollaston in 1802, rediscovered by Joseph von Fraunhofer in 1814, and identified by Gustav Kirchhoff and Robert Bunsen in the 1860s as signals indicating the existence of specific chemical elements.

The pioneering work of Indian astrophysicist Meghnad Saha in 1920 linked the intensity of these "absorption lines" with the temperature and chemical composition of stars, which laid the foundation for our stellar physical model. Cecilia Payne gaposchkin realized from this foundation that stars like our sun are mainly composed of hydrogen and helium and have only a small amount of heavier chemical elements.

Since then, fundamental calculations that link the spectral characteristics with the chemical composition and physics of stellar plasma have brought vital significance to astrophysics. They are the basis for a century of progress in our understanding of the chemical evolution of the universe and the physical structure and evolution of stars and exoplanets. That's why the different pieces of the puzzle don't match when new observations become available and provide insight into the inner workings of our sun, which is shocking.

The modern standard model of solar evolution is calibrated with a group of well-known measurement data of solar atmospheric chemical composition published in 2009. However, in some important details, the reconstruction of the star's internal structure based on the standard model is inconsistent with another set of measurement results: solar seismic data, that is, the measurement results that track the small oscillation of the whole sun very accurately -- the sun expands and contracts rhythmically in a unique mode, and the time scale is between seconds and hours.

Just as seismic waves provide geologists with important information about the interior of the earth or just as bells encode information about its shape and material properties, solar seismology provides information about the interior of the sun.

Highly accurate solar seismic measurements give results about the internal structure of the sun, which is contrary to the standard solar model. According to solar seismology, the so-called convective region inside the sun, that is, the material rises and sinks again, just like the water in a boiling pot, is much larger than predicted by the standard model. The sound wave velocity near the bottom of the region also deviates from the prediction of the standard model, as does the total amount of helium in the sun. Most importantly, some measurements of solar neutrinos -- these transient elementary particles, which are difficult to detect and arrive directly from the core of the sun -- also have slight deviations from the experimental data.

Astronomers soon had their "solar abundance crisis", and in order to find a way out, some suggestions were unusual to completely strange. Did the sun add some metal poor gas during its planetary formation? Is energy transported by non interacting dark matter particles?

The latest research published by Ekaterina MAG, Maria Bergemann and their colleagues has successfully solved this crisis by re examining the model based on which the spectral estimation of the solar chemical composition is based. Early studies of how stellar spectra are produced relied on something called local thermal equilibrium. They assume that in each region of a star's atmosphere, energy has time to diffuse and reach an equilibrium. This will make it possible to assign a temperature to each such region, which brings considerable simplification to the calculation of common coupling.

But as early as the 1950s, astronomers had realized that this situation was too simplified. Since then, more and more studies have included non LTE calculations and abandoned the assumption of local equilibrium. Non LTE calculations include a detailed description of how energy is exchanged within the system -- atoms are excited by photons, or collide, and photons are emitted, absorbed, or scattered. In the stellar atmosphere, because the density is too low to make the system reach thermal equilibrium, this attention to detail will be rewarded. There, the results of non LTE calculations are significantly different from their local equilibrium calculations.

Maria Bergemann of the Max Planck Institute of astronomy is one of the world leaders in applying nonlinear computing to stellar atmospheres. As part of her doctoral work in the group, Ekaterina MAG began to calculate in more detail the interaction of radioactive substances in the solar photosphere. The photosphere is the source of most of the sun's rays and the outer layer where the absorption lines are printed on the solar spectrum.

In this study, they tracked all the chemical elements related to the current model of how stars evolve over time, and applied a variety of independent methods to describe the interaction between solar atoms and radiation fields to ensure that the results are consistent. To describe the convective region of the sun, they used existing simulations that took into account both the physics of plasma motion and radiation. In order to compare with spectral measurements, they selected the data set with the highest quality: the solar spectrum published by the Institute of Astrophysics and Geophysics of the University of Gottingen. "We have also paid extensive attention to the analysis of statistical and systemic effects that may limit the accuracy of the results," MAG said

The new calculation results show that the relationship between the abundances of these key chemical elements and the intensity of the corresponding spectral lines is very different from what researchers previously said. Therefore, the chemical abundances obtained from the observed solar spectra are somewhat different from those described in previous analyses.

"We found that, according to our analysis, the sun contains 26% more elements than helium, which is heavier than previously inferred," MAG explained. In astronomy, this element heavier than helium is called "metal". Only one thousandth of all the nuclei of the sun are metals; It is this very small number that has now changed the previous value by 26%. MAG added: "the oxygen abundance value is nearly 15% higher than that in previous studies." However, the new values are consistent with the chemical composition of primitive meteorites, which are believed to represent the chemical composition of the very early solar system.

When these new values are used as inputs to the current solar structure and evolution models, the puzzling differences between the results of these models and solar seismic measurements disappear. MAG, Bergemann and their colleagues have made an in-depth analysis of how spectral lines are generated and tried to solve the solar abundance crisis by relying on a fairly complete model of basic physics.

Maria Bergemann said: "new solar models based on our new chemical composition are more realistic than ever: they produce solar models that are consistent with all the information we have about the current structure of the sun - sound waves, neutrinos, luminosity and solar radius - but do not require non-standard and strange physics inside the sun."

As an added benefit, the new model can be easily applied to stars other than the sun. At a time when large-scale surveys such as sdss-v and 4MOST are providing high-quality spectra for more and more stars, this progress is indeed of great value - making future stellar chemical analysis and their broader impact on the reconstruction of the chemical evolution of our universe more firmly established than ever before.

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