- 3269 - STARS - what we learn from stardust? Stars have life cycles too. They are born when bits of dust and gas floating through space find each other and collapse in on each other and heat up. They burn for millions to billions of years, and then they die.
----------------------------- 3269 - STARS - what we learn from stardust?
- When stars die, they pitch the particles that formed in their winds out into space, and those bits of stardust eventually form new stars, along with new planets and moons and meteorites.
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- In a meteorite that fell fifty years ago in Australia, scientists have now discovered stardust that formed 5 to 7 billion years ago. That is the oldest solid material ever found on Earth. They tell us about how stars formed in our galaxy.
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- The materials are called “presolar grains-minerals”. They were formed before the Sun was born. They are solid samples of stars, real stardust. These bits of stardust became trapped in meteorites where they remained unchanged for billions of years, making them time capsules of the time before our solar system..
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- But presolar grains are rare. They are found only in about five percent of meteorites that have fallen to Earth, and they're tiny. A hundred of the biggest ones would fit on the period at the end of this sentence.
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- But the Field Museum has the largest portion of the Murchison meteorite, a treasure trove of presolar grains that fell in Australia in 1969. Presolar grains were isolated from the Murchison meteorite for this study about 30 years ago at the University of Chicago.
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- It starts with crushing fragments of the meteorite down into a powder. Once all the pieces are segregated, it's a kind of paste, and it has a pungent characteristic. This meteorite paste is then dissolved with acid, until only the presolar grains remained.
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- Once the presolar grains were isolated, the researchers figured out from what types of stars they came and how old they were. The researchers use “exposure age data“, which basically measures their exposure to cosmic rays, which are high-energy particles that fly through our galaxy and penetrate solid matter.
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- Some of these cosmic rays interact with the matter and form new elements. And the longer they get exposed, the more those elements form. By measuring how many of these new cosmic-ray produced elements are present in a presolar grain, science can tell how long it was exposed to cosmic rays, which tells us how old it is.
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- The researchers learned that some of the presolar grains in their sample were the oldest ever discovered-based on how many cosmic rays they'd soaked up, most of the grains had to be 4.6 to 4.9 billion years old, and some grains were even older than 5.5 billion years. Our Sun is 4.6 billion years old, and Earth is 4.5 billion.
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- Since presolar grains are formed when a star dies, they can tell us about the history of stars. They have more young grains that we expected. The hypothesis is that the majority of those grains, which are 4.9 to 4.6 billion years old, formed in an episode of enhanced star formation. There was a time before the start of the Solar System when more stars formed than normal.
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- Thanks to these grains, we now have direct evidence for a period of enhanced star formation in our galaxy seven billion years ago with samples from meteorites. In examining the way that the minerals in the grains interacted with cosmic rays, the researchers also learned that presolar grains often float through space stuck together in large clusters.
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- This study has directly determined the lifetimes of stardust. Astronomers are looking at the history of our galaxy. Stardust is the oldest material to reach Earth, and from it, we can learn about our parent stars, the origin of the carbon in our bodies, the origin of the oxygen we breathe. With stardust, we can trace that material back to the time before the Sun was born.
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- September 6, 2021 STARS - what we learn from stardust? 3269
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--------------------- --- Tuesday, September 7, 2021 ---------------------------
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