Wednesday, August 18, 2021

Supernovas may have helped to spread radioactive elements in the Solar System

Astronomers already have a good idea, supported by computer simulations, of how planetary systems form and receive radioactive elements sent by supernova explosions. Now, a new study has obtained observational data in a system close to ours, which further strengthens this model.

 Located just 460 light-years from the Solar System, the Ophiuchus star-forming complex emits gamma rays that betray the presence of the short-lived aluminum-26 radionuclide. A radionuclide is the radioactive form of an element—in this case, aluminum—that is, an unstable atom that stabilizes when it releases energy in the form of radiation.


But what does aluminum-26 have to do with the formation of star systems? Well, in the 1970s, scientists discovered inclusions in meteorites caused by the decay of short-lived radionuclides. This is strange, because “short life” in the case of aluminum-26, for example, means something like 717,000 years. Therefore, any atom of this element that may have existed at the beginning of the Solar System, 4.6 billion years ago, has long since stabilized.


However, there were the short-lived radionuclide signals present in meteorites, making scientists scratch their heads, asking "where did they come from?" The most likely answer is supernovae, massive star explosions capable of fusing heavy elements. More precisely, elements number 6 to 40 on the periodic table.

The next question is: where are these supernovas that sent these radioactive elements here? This is where the Ophiuchus star formation complex comes in. It is a "nursery" of stars, where the most massive explode early and release radiation, which in turn mixes with stars still in the process of formation. Looking at the complex at various wavelengths, the authors of the new study noticed a flux of aluminum-26 in a nearby star cluster.

This cluster has hosted supernovae and is therefore rich in heavy elements. "The enrichment process we are seeing in Ophiuchus is consistent with what happened during the formation of the Solar System 5 billion years ago," said astrophysicist John Forbes of the Flatiron Institute.

He explains that when his team saw “this beautiful example of how the process can happen,” they soon began to model this cluster on a computer to simulate a formation of star systems. As a result, they found that there is a 59% chance that aluminum-26 will be produced by a supernova and a 68% chance that there will be several supernovas in this process.

For Forbes, this is “important for the early evolution of planetary systems, as 26-aluminium is the main source of early heating. More aluminum-26 probably means drier planets.” He claims that many star systems will be born with large amounts of aluminum-26, but with huge variations. The research was published in Nature Astronomy.

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