3589 - STARS - chemical elements in Stars? Astronomers find a star that contains 65 different “Elements”. Chemical elements are listed in the “Periodic Table of Elements“. There are 88 natural elements and up to some 103 that can be created in radioactive research.
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--------------------- 3589 - STARS - chemical elements in Stars?
- We know that gold comes from stars. All stars are comprised primarily of hydrogen and helium. But they contain other elements, which astrophysicists refer to as a star’s metallicity. Our Sun has a high metallicity and contains 67 different elements, including about 2.5 trillion tons of gold. That’s right 2,500,000,000,000 tons.
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- Astronomers have found a distant star that contains 65 elements, the most ever detected in another star. Gold is among the elements discovered. This star was a fairly bright star in our neighborhood of the Milky Way, named” HD 222925“.
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- It is close to the southern sky’s Tucana (Toucan) constellation. Astronomers are calling it the “gold standard” star because it’s their best opportunity to study how stars create some of the heavy elements in the Universe. That process is called the “r-process“, or “rapid neutron capture process“.
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- HD 222295 is an r-process enhanced but metal-poor star. It has high metallicity, meaning it contains many elements other than hydrogen and helium, but not much of those elements by mass.
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- It’s not the first one discovered. “CS 22892–052“, “Sneden’s star“, namedd after the scientist who first identified 53 chemical elements in it. But HD 222295 is much brighter in UV than Sneden’s star, making it much easier to observe spectroscopically. Spectroscopy is how the researchers were able to identify these 65 different elements.
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- Each element in the periodic table will absorb or emit light at different wavelengths depending the orbits of that elements electrons. If you measure the absorption lines in the elements spectrum you can identify that element. This process is called spectroscopy.
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- What makes this star so unique is that it has a very high relative proportion of the elements listed along the bottom two-thirds of the periodic table. These heavier elements were made by the “rapid neutron capture process“. Astronomers are trying to study the physics to understanding how, where and when those heavier elements were created.
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- There are two types of neutron capture: the “slow neutron capture process“, or “s-process“, and the “r-process“. The s-process is reasonably well-understood, but scientists still have significant questions about the r-process. Astrophysicists have a good theoretical understanding of the r-process, but it wasn’t observed directly until 2019 when observers saw strontium in a kilonova explosion. Kilonova is a more explosive type of supernova explosion.
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- Rapid neutron capture allows an atomic nucleus to capture neutrons quicker than the neutrons can decay, creating heavy elements. The r-process begins with elements lighter than iron. In an environment with lots of neutrons and lots of energy, these lighter elements can capture neutrons since they’re neutral and have no charge.
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- When an atom captures a neutron, it emits an electron, converting the neutron into another proton. That raises the atomic number, and the lighter element becomes a heavier element.
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- These heavier elements, including gold, are rarely detected in stars because the astrophysical sites that have the r-process are rare. You need lots of neutrons that are free and a very high energy set of conditions to liberate them and add them to the nuclei of atoms.
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- This rarity makes the r-process challenging to study, and also what makes the heavier elements, like gold, rare. Neutron star mergers and the resulting kilonova explosions are one of the environments that foster the r-process.
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- Supernovae explosions of massive stars are the other. Nailing down the astrophysical environments that allow the r-process is critical in understanding the r-process.
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- HD 222295 didn’t produce the heavy elements it contains. They were produced earlier in the Universe and then spread into space by either supernovae or kilonovae. Then they were taken up in another generation of star formation, in this case by HD 222295.
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- Scientists know that the r-process is one of the main ways stars and their remnants produce heavier elements with atomic numbers greater than 30. Observations have confirmed that the r-process occurs in neutron star mergers and the resulting kilonova explosions. But there are still some open questions that have persisted for a long time, like which elements it produces and in what abundances?
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- In 2019, a team of European researchers found signatures of strontium formed in a neutron-star merger. Researcher’s questions have led to the creation of the “R-Process Alliance“, a group of scientists trying to find answers.
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- The researchers think that HD 222295 is one of a group of stars that formed in an environment enriched by the r-process. The star’s metallicity is higher than most known stars enriched by the r-process. That suggests that multiple supernovae enriched it. HD 222295 likely didn’t form as part of the Milky Way but was captured by our galaxy at some point in the past.
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- Now that astrophysicists have identified a bright star containing elements from the r-process, it can act as a proxy for what supernovae and kilonovae produce. As researchers create models of the r-process inside these events that creates the heavy elements, those models must have the same signature as HD 222295.
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- Gold has always held a certain mystique for humanity. It’s unique among the elements and made regular appearances in the world’s myths. In ancient Greece, the Gods dressed in gold and golden apples conferred mortality on those who ate them if they could get past the dragon that guarded them. In Hindu mythology, gold is the source of power and can transmit divine consciousness.
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- The ancients treasured gold, but they couldn't have guessed at its origins. King Tut's mask and his inner coffin. The inner coffin is solid gold and weighs almost 243 pounds.
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- Those beliefs are wiped away now, lost to time. But the science that replaces them is even more fascinating. The ancients could never have imagined that their myths would be replaced by science and that stars could explode and create gold and other elements.
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- They could never have envisioned gigantic mountain-top telescopes that peer vast distances into space. They could never have imagined that we could cut up a star’s light and determine that the star holds gold.
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- And they could never have guessed that our own Sun contains 2.5 trillion tons of gold.
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May 28, 2022 STARS - chemical elements in Stars? 3589
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