Elemental abundance in the universe
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Elemental Abundance in the Universe
Overview of Elemental Abundance
Elemental abundance in the universe refers to the distribution and quantity of chemical elements found throughout the cosmos. This distribution is crucial for understanding the formation and evolution of stars, planets, and galaxies. The elemental abundance is often measured in various celestial bodies, including stars, meteorites, and the interstellar medium.
Historical Context and Early Studies
The foundational work on elemental abundance was conducted by Suess and Urey in 1956, who created an elemental abundance table that has been refined over the years as more reliable data became available. Despite some changes, the original abundances and their variations with mass numbers have remained remarkably consistent .
Solar System Elemental Abundances
The Sun, containing more than 99% of the mass in the solar system, serves as a good proxy for the overall composition of the solar system. Studies have shown that the solar system's composition reflects the molecular cloud from which it formed 4.567 billion years ago. This composition is critical for testing nucleosynthesis models and understanding galactic chemical evolution .
New abundance tables for Cl chondrites and the solar photosphere have been compiled, showing that most elements agree within 9% accuracy between the Sun and meteorites, with significant discrepancies only for a few elements like Fe, Mn, Ge, Pb, and W .
Galactic Elemental Abundance Ratios
The SDSS/APOGEE survey has mapped the trends of elemental abundance ratios across the Galactic disk for 15 elements in a sample of over 20,000 stars. This study found that the median trends of [X/Mg] versus [Mg/H] are nearly independent of location in the Galaxy, suggesting a relatively simple picture of abundance ratio variations. These trends can provide strong tests of supernova nucleosynthesis calculations .
Radial Distribution in the Galactic Disc
The Gaia-ESO Survey has traced the radial distributions of elements produced through different nucleosynthetic channels, such as α-elements (O, Mg, Si, Ca, Ti) and iron-peak elements (Fe, Cr, Ni, Sc). The study found that the spatial distributions of these elements' abundance ratios are consistent with a chemo-dynamical Galactic evolutionary model, highlighting the complex and diverse nucleosynthesis of various α-elements .
Elemental Abundances in Meteorites and the Sun
A review of abundance information for elements in meteorites and the Sun has led to the compilation of a new table of elemental abundances characteristic of the primitive solar nebula. This table emphasizes the poorly determined abundances in the silicon-to-calcium region, which impact theories of nucleosynthesis .
Neutron Capture Processes and Heavy Elements
Chemodynamical simulations have examined the distributions of elemental abundance ratios, including heavy neutron-capture elements like Europium (Eu). The study found that neutron star mergers and magneto-rotational supernovae are significant contributors to these elements, while electron-capture supernovae and neutrino-driven winds are less effective .
Conclusion
The study of elemental abundance in the universe provides critical insights into the processes of stellar nucleosynthesis, the formation of celestial bodies, and the evolution of galaxies. From the early work of Suess and Urey to modern surveys like SDSS/APOGEE and Gaia-ESO, our understanding of elemental distribution continues to evolve, offering a clearer picture of the cosmos and its intricate chemical makeup.
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