- 3375 - STAR DUST - that made the Universe? All the matter we see around us here on Earth, even our own bodies, has gone through at least one cycle of stellar birth and death, maybe more. But which type of star was it?
--------------------- 3375 - STAR DUST - that made the Universe?
- We know we’re made of stardust. But , did it come from “Red Giant stars“? When you drink a glass of water, that water has already been through a bunch of other people’s digestive tracts. Maybe Attila the Hun’s or Vlad the Impaler’s; maybe even a Tyrannosaurus Rex’s.
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- The same thing is true of stars and matter. All the matter we see around us here on Earth, even our own bodies, has gone through at least one cycle of stellar birth and death, maybe more. But which type of star was it?
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- The story of our Solar System started about 4.5 billion years ago when a molecular cloud collapsed. At the center of that collapsed cloud the Sun came to life in a burst of fusion, and a disc of gas and dust formed around it. Eventually, all of the planets in our Solar System formed from that proto-planetary disc.
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- Within that disc of material were dust grains that had formed around certain other stars. These special grains were distributed unevenly throughout the disc, like salt and pepper. As the planets of the Solar System formed, each one contained its own mixture of gas and dust, and of those special grains of “ salt and pepper“.
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- Planets coalesce out of the remaining molecular cloud the star formed out of. Within this accretion disk lay the fundamental elements necessary for planet formation and potential life.
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- Advances in measuring techniques allow scientists to detect the material the planets formed from, and to determine its origin. It all comes down to isotopes. An isotope is an atom of a given element with the same number of protons in its nucleus, but a different number of neutrons.
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- For example, there are different isotopes of carbon, like C13 and C14. While all carbon isotopes have 6 protons, C13 has 7 neutrons while C14 has 8 neutrons. The mixture of different isotopes in a planet, not just of carbon but of other elements as well, is like a fingerprint. And that fingerprint can tell scientists a lot about a body’s origins.
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- Stardust has really extreme, unique fingerprints, and because it was spread unevenly through the proto-planetary disc, each planet and each asteroid got its own fingerprint when it was formed.
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- Over the years, scientists have been studying these fingerprints on Earth and in meteorites. Comparisons between the two reveal how long-dead red giant stars have contributed matter to the formation of Earth and everything on it. Including us.
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- Scientists have been able to compare these isotopic anomalies between the Earth and meteorites for more and more elements. The scientists focused on the element palladium.
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- Previous studies have examined isotope ratios for other elements, like ruthenium and molybdenum, which are palladium’s neighbors on the periodic table. They expected similar amounts of palladium but got a surprise.
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- The meteorites contained far smaller palladium anomalies than expected. A new model is used to explain these results. This model shows that even though everything in our Solar System was created from stardust, one type of star contributed most to Earth: red giants, or “asymptotic giant branch” (AGB) stars.
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- These are stars in the same mass range as our Sun which expand into red giants when they deplete their hydrogen. Our own Sun will become one of these in about 4 or 5 billion years.
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- As part of their end-state, these stars synthesize elements in what’s called the s-process. The s-process, or slow neutron capture process, creates elements like palladium, and its neighbors on the periodic table, ruthenium and molybdenum. The s-process creates these elements with seeds of iron nuclei, which themselves were created in supernovae in previous generations of stars.
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- Palladium is slightly more volatile than the other elements measured. As a result, less of it condensed into dust around these stars, and therefore there is less palladium from stardust in the meteorites.
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- There is a greater abundance of material from red giants in Earth’s makeup than there is in Mars, or in asteroids like Vesta further out in our Solar System. The outer region contains more material from supernovae.
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- In our young Solar System, dust from red giants resisted evaporation or destruction from the Sun better than dust from supernovae. That's why Earth contains more matter from red giants than bodies further out.
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- When the planets formed, temperatures closer to the Sun were very high. Some of the dust grains were more unstable than others, including ones with icy crusts. That type was destroyed in the inner Solar System, close to the Sun.
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- But, stardust from red giants was more stable and resisted destruction, so it’s more concentrated close to the Sun. That dust from supernova explosions is also prone to evaporate more quickly since its smaller. So there’s less of it in the inner Solar System, and on Earth.
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- This explains why the Earth has the largest enrichment of stardust from red giant stars compared to other bodies in the solar system.
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- Around 4,500,000,000 years ago, an interstellar molecular cloud collapsed. At its center, the Sun was formed; around that, a disc of gas and dust appeared, out of which the earth and the other planets would form.
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- This thoroughly mixed interstellar material included exotic grains of dust, Stardust that had formed around other suns. These dust grains only made up a small percentage of the entire dust mass and were distributed unevenly throughout the disc.
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- Researchers are able to detect the stardust that was present at the birth of our solar system. They examine specific chemical elements and measure the abundance of different isotopes, the different atomic flavors of a given element, which all share the same number of protons in their nuclei but vary in the number of neutrons.
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- The variable proportions of these isotopes act like a fingerprint. Stardust is extremely, unique fingerprints because it was spread unevenly through the proto-planetary disc, each planet and each asteroid got its own fingerprint when it was formed.
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called isotopic anomalies for more and more elements. They have been looking at meteorites that were originally part of asteroid cores that were destroyed a long time ago, with a focus on the element palladium.
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- Other teams had already investigated neighboring elements in the periodic table, such as molybdenum and ruthenium, so scientists could predict what their palladium results would show.
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- But, their laboratory measurements did not confirm the predictions. The meteorites contained far smaller palladium anomalies than expected. Now the researchers have come up with a new model to explain these results.
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- They argue that stardust consisted mainly of material that was produced in red giant stars. These are aging stars that expand because they have exhausted the fuel in their core. Our sun, too, will become a red giant four or five billion years from now.
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- In these stars heavy elements such as molybdenum and palladium were produced by what is known at the slow neutron capture process. Palladium is slightly more volatile than the other elements measured. As a result, less of it condensed into dust around these stars, and therefore there is less palladium from stardust in the meteorites.
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- Another stardust puzzle: the higher abundance of material from red giants on Earth compared to Mars or Vesta or other asteroids further out in the solar system. This outer region saw an accumulation of material from supernova explosions.
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- When the planets formed, temperatures closer to the Sun were very high. This caused unstable grains of dust, those with an icy crust, to evaporate. The interstellar material contained more of this kind of dust that was destroyed close to the Sun, whereas stardust from red giants was less prone to destruction and hence concentrated there.
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- It is conceivable that dust originating in supernova explosions also evaporates more easily, since it is somewhat smaller. This allows us to explain why the Earth has the largest enrichment of stardust from red giant stars compared to other bodies in the solar system. So there!
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December 13, 2021 STAR DUST - that made the Universe? 3375
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