An international team of astronomers, including Stella Offner of the University of Texas at Austin, has proposed a new method for the formation of aluminum-26 in star-forming planetary systems. Because its radioactive decay is thought to be a source of heat for planetary building blocks called planetesimals, it is important for astronomers to know where aluminum-26 comes from. Their research is published in the current publication Astrophysical journal.
“Atoms, such as aluminum and its radioactive isotope aluminum-26, allow us to do the archeology of the solar system,”; Offner said. “Interestingly, the abundance of different atoms today can provide information about the formation of our solar system billions of years ago.”
Since the discovery of the Allende meteorite in 1976, astronomers have debated the origins of large amounts of aluminum-26 in our early solar system. Some said it was blown here by supernova explosions and massive stellar winds. However, these scenarios require a number of chances: Our sun and planets should form at exactly the right distance from massive stars, which are quite rare.
The Offner team suggested an explanation that did not require an external source. They suggest that aluminum-26 be formed close to the young sun on the inner part of the disk forming the surrounding planet. When matter fell from the inner edge of the disk onto the sun, it created waves that emitted high-energy protons called cosmic rays.
Leaving the sun at almost the speed of light, cosmic rays propagated into the surrounding disk, colliding with the isotopes aluminum-27 and silicon-28, turning them into aluminum-26.
Due to a very short half-life of approximately 770,000 years, aluminum-26 had to be formed or mixed into a disk forming a young planet surrounding the sun just before the first solid condensed in our solar system. It plays an important role in shaping planets such as Earth, as it can provide enough heat through radioactive decay to form planetary bodies with a layered interior (such as a solid Earth core with a rocky mantle at the top and a thin crust above it). The radioactive decay of aluminum-26 also helps to dry the early planetary tubes to form poor water rocks.
The ratio of aluminum-26 to the isotope aluminum-27 is fairly constant in the oldest bodies in our solar system, comets and asteroids. Since the discovery of aluminum-26 in meteorites (which are asteroid chips), considerable effort has been directed to find a reliable explanation for both its entry into our early solar system and the fixed ratio of aluminum-26 to aluminum. -27.
The Offner team has focused its research on the transition to the formation of the sun: when the gas surrounding a young star is depleted and the amount of gas entering the sun drops sharply. Almost all young stars have experienced this transition over the last few tens or hundreds of thousands of years of formation.
As our sun set, the rising gas followed the lines of the magnetic field to its surface. This caused a wave of brutal shock, a “shock shock” that accelerated the cosmic rays. These cosmic rays flow outward before hitting the gas into the planet’s forming disk and causing chemical reactions. The researchers calculated different models for this process.
“We have found that a low degree of acrylication can lead to an amount of aluminum-26 and a ratio of aluminum-26 to aluminum-27 in the solar system,” said Brandt Gaches, a lead author at the German University. Cologne.
The proposed mechanism is generally valid for many low-mass stars, including sun-like stars. It is in such systems that astronomers have discovered most of the now-known exoplanets.
“The cosmic rays, which have been accelerated by incorporation into the forming young stars, may form the basis for the enrichment of aluminum-26 in many planetary systems,” Gach concluded. “And this is one of the biggest questions if the proposed acceleration mechanism through shock waves will be observed in the formation of stars.”
By studying exploding stars through an atomic nucleus
Brandt AL Gaches et al. Enrichment of aluminum-26 on the surface of star disks due to the cosmic rays of the precursors, Astrophysical journal (2020). DOI: 10.3847 / 1538-4357 / ab9a38
Provided by the University of Texas at Austin
Citation: When studying radioactive aluminum in stellar systems, the secrets of formation are unlocked (July 29, 2020). July 29 From https://phys.org/news/2020-07-radioactive-aluminium-stellar-formation-secrets.html
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