SPACE/COSMOS
New measurements of solar radiative opacity thanks to helioseismology
Researchers have developed an innovative method using helioseismology to measure solar radiative opacity under extreme conditions
University of Liège
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SOHO's EIT (Extreme ultraviolet Imaging Telescope) images the solar atmosphere at several wavelengths and, therefore, shows solar material at different temperatures. In the images taken at 304 Angstroms, the bright material is at 60 000 to 80 000K. In those taken at 171, at 1 million Kelvin. 195 Angstrom images correspond to about 1.5 million Kelvin. The hotter the temperature, the higher you look in the solar atmosphere
view moreCredit: SOHO instrument consortium
Researchers have pioneered an innovative method using helioseismology to measure the solar radiative opacity under extreme conditions. This groundbreaking work, published in Nature Communications, not only reveals gaps in our understanding of atomic physics but also confirms recent experimental results, thereby opening new perspectives in astrophysics and nuclear physics.
Helioseismology is a discipline dedicated to studying the Sun's acoustic oscillations, enabling us to probe the interior of our star with remarkable precision. By analysing these waves, it is possible to reconstruct fundamental parameters such as the density, temperature, and chemical composition of the Sun's plasma—essential elements for understanding how our star works and evolves. This method transforms the Sun into a true astrophysical laboratory, providing crucial data for refining stellar models and better understanding the evolution of stars in the Universe.
A new international study, led by Gaël Buldgen, a researcher at the University of Liège, has used helioseismic techniques to provide an independent measurement of the absorption of high-energy radiation by the solar plasma in the deep layers of its structure. This collaborative work sheds new light on solar radiative opacity, a crucial physical quantity for understanding the interaction between matter and radiation in the extreme conditions of the Sun's interior. The results confirm observations made in renowned American laboratories such as the Sandia National Laboratories and ongoing efforts at the Livermore National Laboratory, while revealing persistent gaps in our understanding of atomic physics and differences between the predictions of research groups at the Los Alamos National Laboratory, the Ohio State University and the research centre of the CEA Paris-Saclay in France.
Unprecedented precision in stellar modelling
The scientific team used advanced numerical tools developed at ULiège, drawing on the university's expertise in helioseismology and stellar modelling. "By detecting the Sun's acoustic waves with unparalleled precision, we can reconstruct our star's internal properties, in much the same way as we would deduce the characteristics of a musical instrument from the sounds it produces", explains Gaël Buldgen.
The precision of helioseismic measurements is exceptional: they allow us to estimate the mass of a cubic centimetre of matter inside the Sun with an accuracy surpassing that of a high-precision kitchen scale without ever seeing or touching the matter. Helioseismology, developed at the end of the twentieth century, has played a major role in advancing fundamental physics. In particular, it has contributed to major discoveries, such as neutrino oscillations, which the 2015 Nobel Prize recognised. These advances demonstrated that solar models were not to blame for the origin of this phenomenon. Still, adjustments were needed with the revision of the solar chemical composition in 2009, confirmed in 2021. This revision caused a crisis in solar models, which no longer agreed with the helioseismic observations.
To meet this challenge, advanced tools have been developed at the University of Liège, initially as part of doctoral work (1), and then enriched through international collaborations in Birmingham and Geneva. These tools have made it possible to revisit the internal thermodynamic conditions of the Sun and to reopen an issue that the scientific community had somewhat neglected. At the same time, the work carried out in 2015 by James Bailey at Sandia National Laboratory highlighted the crucial role of radiative opacity. The first experimental measurements were first met with some skepticism, as they revealed significant differences with theoretical predictions.
Today's helioseismic measure provides valuable confirmation and makes it possible to specify the temperature, density and energy regimes in which these experiments should be concentrated in order to better reproduce solar conditions. In addition, the Z Machine experiments, although extremely valuable, have prohibitive energy and financial costs. Helioseismic measurements, on the other hand, offer an economical and complementary alternative while guiding experimentalists towards optimal windows for their laboratory measurements.
The implications of this research extend far beyond stellar modelling. It improves the accuracy of the theoretical models used to estimate the age and mass of stars and exoplanets, thereby contributing to our understanding of galactic evolution and stellar populations. "The Sun is our great calibrator of stellar evolution, our preferred laboratory for finding out whether we are on the right track, or not. These results are even more important as we prepare to launch the PLATO satellite in 2026, one of the objectives of which is to accurately characterize solar-type stars to find habitable terrestrial planets. What's more, these results have resonances in nuclear fusion, as the Sun remains the only stable nuclear fusion reactor in our solar system. Improving our understanding of the Sun's internal conditions directly impacts fusion energy research, a key issue in the development of clean energy solutions," adds Gaël Buldgen.
A call for refined theoretical models
The results highlight the need to improve existing atomic models to resolve the discrepancies between experimental observations and theoretical calculations. These advances should redefine our understanding of stellar evolution and the physical processes that govern the structure and evolution of stars. This research confirms the University of Liège's position at the cutting edge of astrophysical science, demonstrating the key role of helioseismology in unlocking the mysteries of the cosmos.
ESA’s mission Plato, PLAnetary Transits and Oscillations of stars, will use its 26 cameras to study terrestrial exoplanets in orbits up to the habitable zone of Sun-like stars. The mission will discover the sizes of exoplanets and discover exomoons and rings around them. Plato will also characterise their host stars by studying tiny light variations in the starlight it receives.
Credit
The Z machine, the largest X-ray generator in the world, is located in Albuquerque, New Mexico. As part of the Pulsed Power Program, which started at Sandia National Laboratories in the 1960s, the Z machine concentrates electrical energy and turns it into short pulses of enormous power, which can then be used to generate X-rays and gamma rays.
Credit
Randy Montoya/Sandia National Laboratories
Scientific reference
1) Gaël Buldgen, Patrick Eggenberger, Vladimir A.Baturin, Thierry Corbard, Joergen Christensen-Dalsgaard, Sébastien Salmon, Arlette Noels, Anna, V., Oreshina, Richard Scuflaire Seismic solar models from Ledoux discriminant inversions, Astronomy & Astrophysics, 2020, Volume 642, id.A36, pp.
Journal
Nature Communications
Article Title
Helioseismic inference of the solar radiative opacity
Article Publication Date
27-Jan-2025
SwRI-designed experiments corroborate theory about how Titan maintains its atmosphere
Laboratory experiments produced gases similar to those on Saturn’s moon
Southwest Research Institute
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To understand the persistent thick atmosphere on Saturn’s largest moon, SwRI worked with the Carnegie Institution for Science Laboratory to create conditions mimicking those at Titan’s rocky core. These laboratory experiments heated and pressurized tubes of organics, producing nitrogen and methane, gases necessary to maintain Titan’s atmosphere.
view moreCredit: Southwest Research Institute
SAN ANTONIO — January 27, 2025 – Southwest Research Institute partnered with the Carnegie Institution for Science to perform laboratory experiments to better understand how Saturn’s moon Titan can maintain its unique nitrogen-rich atmosphere. Titan is the second largest moon in our solar system and the only one that has a significant atmosphere.
“While just 40% the diameter of the Earth, Titan has an atmosphere 1.5 times as dense as the Earth’s, even with a lower gravity,” said SwRI’s Dr. Kelly Miller, lead author of a paper about these findings published in the journal Geochimica et Cosmochimica Acta. “Walking on the surface of Titan would feel a bit like scuba diving.”
The origin, age, and evolution of this atmosphere, which is roughly 95% nitrogen and 5% methane, has puzzled scientists since it was discovered in 1944.
“The presence of methane is critical to the existence of Titan’s atmosphere,” Miller says. “The methane is removed by reactions caused by sunlight and would disappear in about 30 million years after which the atmosphere would freeze onto the surface. Scientists think an internal source must replenish the methane, or else the atmosphere has a geologically short lifetime.”
Miller was also the lead author of a 2019 paper published in the Astrophysical Journal that proposed a theoretical model of how the atmosphere may have developed and is replenished over the years. The paper theorizes that large amounts of highly complex organic materials are heated up in Titan’s rocky interior, releasing nitrogen as well as carbon gases like methane. The gas then seeps out at the surface, where it forms a thick atmosphere around the moon. This theory is corroborated by the recent experiments that heated organic materials to temperatures of 250 to 500 Celsius at pressures up to 10 kilobars to simulate the interior conditions of Titan. The experiments produced carbon gases like carbon dioxide and methane in sufficient quantities to help supply Titan’s atmospheric reservoir.
The paper is largely based on data from NASA’s Cassini-Huygens spacecraft mission, which launched in 1997 and explored the Saturn system from 2004 to 2017. NASA plans to launch its next mission to the Saturnian system in 2028 with a spacecraft dubbed Dragonfly. It will include a quadcopter designed to explore Titan up close and investigate whether environments at Titan could have ever been conducive for life. Miller is working next with a global team of researchers to study the habitability of the subsurface liquid ocean.
To access the Geochimica et Cosmochimica Acta paper “Experimental heating of complex organic matter at Titan’s interior conditions supports contributions to atmospheric N2 and CH4” see http://doi.org/10.1016/j.gca.2024.12.026 (link is external).
For more information, visit https://www.swri.org/planetary-science.
Journal
Geochimica et Cosmochimica Acta
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Experimental heating of complex organic matter at Titan’s interior conditions supports contributions to atmospheric N2 and CH4
Article Publication Date
1-Feb-2025
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