From The MPG Institute for the Advancement of Science [MPG zur Förderung der Wissenschaften e. V] (DE).: “The chemistry of the Sun” 

: From The MPG Institute for the Advancement of Science [MPG zur Förderung der Wissenschaften e. V] (DE).

May 20, 2022

Contacts:
Dr. Markus Pössel
Head of press and public relations
Max Planck Institute for Astronomy, Heidelberg
+49 6221 528-261
pr@mpia.de

Ekaterina Magg
Max Planck Institute for Astronomy, Heidelberg
+49 6221 528-392
semenova@mpia.de

Dr. Maria Bergemann
Max Planck Institute for Astronomy, Heidelberg
+49 6221 528-401
bergemann@mpia.de

Astronomers have resolved the decade-long solar abundance crisis: the conflict between the internal structure of the Sun as determined from solar oscillations (helioseismology) and the structure derived from the fundamental theory of stellar evolution, which in turn relies on measurements of the present-day Sun’s chemical composition. New calculations of the physics of the Sun’s atmosphere yield updated results for abundances of different chemical elements, which resolve the conflict. Notably, the Sun contains more oxygen, silicon and neon than previously thought. The methods employed also promise considerably more accurate estimates of the chemical compositions of stars in general.

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Spectrum of the Sun, taken with the NARVAL very high-resolution spectrograph installed at the Télescope Bernard Lyot, Observatoire Midi-Pyrénées. Spectra such as this, in particular the properties of the dark absorption lines that are clearly visible in this image, allow astronomers to deduce a star’s temperature and chemical composition. © M. Bergemann / MPIA / NARVAL@TBL

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Télescope Bernard Lyot (Pic du Midi Observatory)

What do you do when a tried-and-true method for determining the Sun’s chemical composition appears to be at odds with an innovative, precise technique for mapping the Sun’s inner structure? That was the situation facing astronomers studying the Sun – until new calculations that have now been published [Astronomy & Astrophysics] by Ekaterina Magg, Maria Bergemann and colleagues, and that resolve the apparent contradiction.

The tried-and-true method in question is spectral analysis. In order to determine the chemical composition of our Sun, or of any other star out there, astronomers routinely turn to spectra: the rainbow-like decomposition of light into its different wavelengths. Stellar spectra contain conspicuous, sharp dark lines, first noticed by William Wollaston in 1802, famously rediscovered by Joseph von Fraunhofer in 1814, and identified as tell-tale signs indicating the presence of specific chemical elements by Gustav Kirchhoff and Robert Bunsen in the 1860s.

Pioneering work by the Indian astrophysicist Meghnad Saha in 1920 related the strength of those “absorption lines” to stellar temperature and chemical composition, providing the basis for our physical models of stars. Cecilia Payne-Gaposchkin’s realization that stars like our Sun consist mainly of hydrogen and helium, with no more than trace amounts of heavier chemical elements, is based on that work.

The underlying calculations relating spectral features to the chemical composition and physics of the stellar plasma have been of crucial importance to astrophysics ever since. They have been the foundation of a century-long progress in our understanding of the chemical evolution of the universe as well as of the physical structure and evolution of stars and exoplanets. That is why it came as something of a shock when, as new observational data became available and provided an insight into the inner workings of our Sun, the different pieces of the puzzle apparently did not fit together.

The modern standard model of solar evolution is calibrated using a famous (in solar physics circles) set of measurements of the solar atmosphere’s chemical composition, published in 2009. But in a number of important details, a reconstruction of our favorite star’s inner structure based on that standard model contradicts another set of measurements: helioseismic data, that is, measurements that track very precisely the minute oscillations of the Sun as a whole – the way that the Sun rhythmically expands and contracts in characteristic patterns, on time scales between seconds and hours.

Just like seismic waves provide geologists with crucial information about the Earth’s interior, or like the sound of a bell encodes information about its shape and material properties, helioseismology provides information about the interior of the Sun.

Highly accurate helioseismic measurements gave results about the Sun’s interior structure that were at odds with the solar standard models. According to helioseismology, the so-called convective region within our Sun where matter rises and sinks down again, like water in a boiling pot, was considerably larger than the standard model predicted. The speed of sound waves near the bottom of that region also deviated from the standard model’s predictions, as did the overall amount of helium in the Sun. To top it off, certain measurements of solar neutrinos – fleeting elementary particles, hard to detect, reaching us directly from the Sun’s core regions – were slightly off compared to experimental data, as well.

Astronomers had what they soon came to call a “solar abundances crisis,” and in search of a way out, some proposals ranged from the unusual to the downright exotic. Did the Sun maybe accrete some metal-poor gas during its planet-forming phase? Is energy being transported by the notoriously non-interacting dark matter particles?

The newly published study by Ekaterina Magg, Maria Bergemann and colleagues has managed to resolve that crisis, by revisiting the models on which the spectral estimates of the Sun’s chemical composition are based. Early studies of how the spectra of stars are produced had relied on something known as local thermal equilibrium. They had assumed that locally, energy in each region of a star’s atmosphere has time to spread out and reach a kind of equilibrium. This would make it possible to assign to each such region a temperature, which leads to a considerable simplification in the calculations.

But as early as the 1950s, astronomers had realized that this picture was oversimplified. Since then, more and more studies incorporated so-called Non-LTE calculations, dropping the assumption of local equilibrium. The Non-LTE calculations include a detailed description of how energy is exchanged within the system – atoms getting excited by photons, or colliding, photons getting emitted, absorbed or scattered. In stellar atmospheres, where densities are far too low to allow the system to reach thermal equilibrium, that kind of attention to detail pays off. There, Non-LTE calculations yield results that are markedly different from their local-equilibrium counterparts.

Maria Bergemann’s group at the Max Planck Institute for Astronomy is one of the world leaders when it comes to applying Non-LTE calculations to stellar atmospheres. As part of the work on her PhD in that group, Ekaterina Magg set out to calculate in more detail the interaction of radiation matter in the solar photosphere. The photosphere is the outer layer where most of the Sun’s light originates, and also where the absorption lines are imprinted on the solar spectrum.

In this study they tracked all chemical elements that are relevant to the current models of how stars evolved over time, and applied multiple independent methods to describe the interactions between the Sun’s atoms and its radiation field in order to make sure their results were consistent. For describing the convective regions of our Sun, they used existing simulations that take into account both the motion of the plasma and the physics of radiation (“STAGGER” and “CO5BOLD”). For the comparison with spectral measurements, they chose the data set with the highest available quality: the solar spectrum published by the Institute for Astro- and Geophysics, University of Göttingen. “We also extensively focused on the analysis of statistical and systematic effects that could limit the accuracy of out results”, notes Magg.

The new calculations showed that the relationship between the abundances of these crucial chemical elements and the strength of the corresponding spectral lines was significantly different from what previous authors had claimed. Consequently, the chemical abundances that follow from the observed solar spectrum are somewhat different than stated in previous analysis.

“We found, that according to our analysis the Sun contains 26% more elements heavier than helium than previous studies had deduced”, explains Magg. In astronomy, such elements heavier than helium are called “metals”. Only on the order of a thousandth of a percent of all atomic nuclei in the Sun are metals; it is this very small number that has now changed by 26% of its previous value. Magg adds: “The value for the oxygen abundance was almost 15% higher than in previous studies.” The new values are, however, in good agreement with the chemical composition of primitive meteorites (“CI chondrites”) that are thought to represent the chemical make-up of the very early solar system.

When those new values are used as the input for current models of solar structure and evolution, the puzzling discrepancy between the results of those models and helioseismic measurements disappears. The in-depth analysis by Magg, Bergemann and their colleagues of how spectral lines are produced, with its reliance on considerably more complete models of the underlying physics, manages to resolve the solar abundance crisis.

Maria Bergemann says: “The new solar models based on our new chemical composition are more realistic than ever before: they produce a model of the Sun that is consistent with all the information we have about the Sun’s present-day structure – sound waves, neutrinos, luminosity, and the Sun’s radius – without the need for non-standard, exotic physics in the solar interior.”

As an added bonus the new models are easy to apply to stars other than the Sun. At a time where large-scale surveys like SDSS-V and 4MOST are providing high-quality spectra for an ever greater number of stars, this kind of progress is valuable indeed – putting future analyses of stellar chemistry, with their broader implications for reconstructions of the chemical evolution of our cosmos, on a firmer footing than ever before.

See the full article here.

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MPG Society for the Advancement of Science [MPG Gesellschaft zur Förderung der Wissenschaften e. V.] is a formally independent non-governmental and non-profit association of German research institutes founded in 1911 as the Kaiser Wilhelm Society and renamed the Max Planck Society in 1948 in honor of its former president, theoretical physicist Max Planck. The society is funded by the federal and state governments of Germany as well as other sources.

According to its primary goal, the MPG Society supports fundamental research in the natural, life and social sciences, the arts and humanities in its 83 (as of January 2014) MPG Institutes. The society has a total staff of approximately 17,000 permanent employees, including 5,470 scientists, plus around 4,600 non-tenured scientists and guests. Society budget for 2015 was about €1.7 billion.

The MPG Institutes focus on excellence in research. The MPG Society has a world-leading reputation as a science and technology research organization, with 33 Nobel Prizes awarded to their scientists, and is generally regarded as the foremost basic research organization in Europe and the world. In 2013, the Nature Publishing Index placed the MPG institutes fifth worldwide in terms of research published in Nature journals (after Harvard University, The Massachusetts Institute of Technology, Stanford University and The National Institutes of Health). In terms of total research volume (unweighted by citations or impact), the Max Planck Society is only outranked by The Chinese Academy of Sciences [中国科学院](CN), The Russian Academy of Sciences [Росси́йская акаде́мия нау́к](RU) and Harvard University. The Thomson Reuters-Science Watch website placed the MPG Society as the second leading research organization worldwide following Harvard University, in terms of the impact of the produced research over science fields.

The MPG Society and its predecessor Kaiser Wilhelm Society hosted several renowned scientists in their fields, including Otto Hahn, Werner Heisenberg, and Albert Einstein.

History

The organization was established in 1911 as the Kaiser Wilhelm Society, or Kaiser-Wilhelm-Gesellschaft (KWG), a non-governmental research organization named for the then German emperor. The KWG was one of the world’s leading research organizations; its board of directors included scientists like Walther Bothe, Peter Debye, Albert Einstein, and Fritz Haber. In 1946, Otto Hahn assumed the position of President of KWG, and in 1948, the society was renamed the Max Planck Society (MPG) after its former President (1930–37) Max Planck, who died in 1947.

The MPG Society has a world-leading reputation as a science and technology research organization. In 2006, the Times Higher Education Supplement rankings of non-university research institutions (based on international peer review by academics) placed the MPG Society as No.1 in the world for science research, and No.3 in technology research (behind AT&T Corporation and The DOE’s Argonne National Laboratory.

The domain mpg.de attracted at least 1.7 million visitors annually by 2008 according to a Compete.com study.

MPG Institutes and research groups

The MPG Society consists of over 80 research institutes. In addition, the society funds a number of Max Planck Research Groups (MPRG) and International Max Planck Research Schools (IMPRS). The purpose of establishing independent research groups at various universities is to strengthen the required networking between universities and institutes of the Max Planck Society.
The research units are primarily located across Europe with a few in South Korea and the U.S. In 2007, the Society established its first non-European centre, with an institute on the Jupiter campus of Florida Atlantic University (US) focusing on neuroscience.
The MPG Institutes operate independently from, though in close cooperation with, the universities, and focus on innovative research which does not fit into the university structure due to their interdisciplinary or transdisciplinary nature or which require resources that cannot be met by the state universities.

Internally, MPG Institutes are organized into research departments headed by directors such that each MPI has several directors, a position roughly comparable to anything from full professor to department head at a university. Other core members include Junior and Senior Research Fellows.

In addition, there are several associated institutes:

International Max Planck Research Schools

Together with the Association of Universities and other Education Institutions in Germany, the Max Planck Society established numerous International Max Planck Research Schools (IMPRS) to promote junior scientists:

• Cologne Graduate School of Ageing Research, Cologne
• International Max Planck Research School for Intelligent Systems, at the Max Planck Institute for Intelligent Systems located in Tübingen and Stuttgart
• International Max Planck Research School on Adapting Behavior in a Fundamentally Uncertain World (Uncertainty School), at the Max Planck Institutes for Economics, for Human Development, and/or Research on Collective Goods
• International Max Planck Research School for Analysis, Design and Optimization in Chemical and Biochemical Process Engineering, Magdeburg
• International Max Planck Research School for Astronomy and Cosmic Physics, Heidelberg at the MPI for Astronomy
• International Max Planck Research School for Astrophysics, Garching at the MPI for Astrophysics
• International Max Planck Research School for Complex Surfaces in Material Sciences, Berlin
• International Max Planck Research School for Computer Science, Saarbrücken
• International Max Planck Research School for Earth System Modeling, Hamburg
• International Max Planck Research School for Elementary Particle Physics, Munich, at the MPI for Physics
• International Max Planck Research School for Environmental, Cellular and Molecular Microbiology, Marburg at the Max Planck Institute for Terrestrial Microbiology
• International Max Planck Research School for Evolutionary Biology, Plön at the Max Planck Institute for Evolutionary Biology
• International Max Planck Research School “From Molecules to Organisms”, Tübingen at the Max Planck Institute for Developmental Biology
• International Max Planck Research School for Global Biogeochemical Cycles, Jena at the Max Planck Institute for Biogeochemistry
• International Max Planck Research School on Gravitational Wave Astronomy, Hannover and Potsdam MPI for Gravitational Physics
• International Max Planck Research School for Heart and Lung Research, Bad Nauheim at the Max Planck Institute for Heart and Lung Research
• International Max Planck Research School for Infectious Diseases and Immunity, Berlin at the Max Planck Institute for Infection Biology
• International Max Planck Research School for Language Sciences, Nijmegen
• International Max Planck Research School for Neurosciences, Göttingen
• International Max Planck Research School for Cognitive and Systems Neuroscience, Tübingen
• International Max Planck Research School for Marine Microbiology (MarMic), joint program of the Max Planck Institute for Marine Microbiology in Bremen, the University of Bremen, the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, and the Jacobs University Bremen
• International Max Planck Research School for Maritime Affairs, Hamburg
• International Max Planck Research School for Molecular and Cellular Biology, Freiburg
• International Max Planck Research School for Molecular and Cellular Life Sciences, Munich
• International Max Planck Research School for Molecular Biology, Göttingen
• International Max Planck Research School for Molecular Cell Biology and Bioengineering, Dresden
• International Max Planck Research School Molecular Biomedicine, program combined with the ‘Graduate Programm Cell Dynamics And Disease’ at the University of Münster and the Max Planck Institute for Molecular Biomedicine
• International Max Planck Research School on Multiscale Bio-Systems, Potsdam
• International Max Planck Research School for Organismal Biology, at the University of Konstanz and the Max Planck Institute for Ornithology
• International Max Planck Research School on Reactive Structure Analysis for Chemical Reactions (IMPRS RECHARGE), Mülheim an der Ruhr, at the Max Planck Institute for Chemical Energy Conversion
• International Max Planck Research School for Science and Technology of Nano-Systems, Halle at Max Planck Institute of Microstructure Physics
• International Max Planck Research School for Solar System Science at the University of Göttingen hosted by MPI for Solar System Research
• International Max Planck Research School for Astronomy and Astrophysics, Bonn, at the MPI for Radio Astronomy (formerly the International Max Planck Research School for Radio and Infrared Astronomy)
• International Max Planck Research School for the Social and Political Constitution of the Economy, Cologne
• International Max Planck Research School for Surface and Interface Engineering in Advanced Materials, Düsseldorf at Max Planck Institute for Iron Research GmbH
• International Max Planck Research School for Ultrafast Imaging and Structural Dynamics, Hamburg

Max Planck Schools

• Max Planck School of Cognition
• Max Planck School Matter to Life
• Max Planck School of Photonics

Max Planck Center

• The Max Planck Centre for Attosecond Science (MPC-AS), POSTECH Pohang
• The Max Planck POSTECH Center for Complex Phase Materials, POSTECH Pohang

Max Planck Institutes

Among others:
• Max Planck Institute for Neurobiology of Behavior – caesar, Bonn
• Max Planck Institute for Aeronomics in Katlenburg-Lindau was renamed to Max Planck Institute for Solar System Research in 2004;
• Max Planck Institute for Biology in Tübingen was closed in 2005;
• Max Planck Institute for Cell Biology in Ladenburg b. Heidelberg was closed in 2003;
• Max Planck Institute for Economics in Jena was renamed to the Max Planck Institute for the Science of Human History in 2014;
• Max Planck Institute for Ionospheric Research in Katlenburg-Lindau was renamed to Max Planck Institute for Aeronomics in 1958;
• Max Planck Institute for Metals Research, Stuttgart
• Max Planck Institute of Oceanic Biology in Wilhelmshaven was renamed to Max Planck Institute of Cell Biology in 1968 and moved to Ladenburg 1977;
• Max Planck Institute for Psychological Research in Munich merged into the Max Planck Institute for Human Cognitive and Brain Sciences in 2004;
• Max Planck Institute for Protein and Leather Research in Regensburg moved to Munich 1957 and was united with the Max Planck Institute for Biochemistry in 1977;
• Max Planck Institute for Virus Research in Tübingen was renamed as Max Planck Institute for Developmental Biology in 1985;
• Max Planck Institute for the Study of the Scientific-Technical World in Starnberg (from 1970 until 1981 (closed)) directed by Carl Friedrich von Weizsäcker and Jürgen Habermas.
• Max Planck Institute for Behavioral Physiology
• Max Planck Institute of Experimental Endocrinology
• Max Planck Institute for Foreign and International Social Law
• Max Planck Institute for Physics and Astrophysics
• Max Planck Research Unit for Enzymology of Protein Folding
• Max Planck Institute for Biology of Ageing