Radionuclides Born Under the Sign of Ofiuco (Planetary Science)

Using multi-wavelength observations – from millimeters to gamma rays – of the star-forming region of Ophiuchus, the astronomers revealed a stream of the aluminum-26 radionuclide from a nearby star cluster. Their discovery indicates that supernovae in the star cluster are the most likely source of short-lived radionuclides in star-forming clouds. All the details on Nature Astronomy

An active star-forming region in the constellation Ofphiuchus is providing astronomers with new insights into the conditions under which the solar system was born. In particular, a new study shows that concerns him directly how the solar system may have been enriched with radioactive elements in the short life (in English short-lived radionuclide , elements whose average life is less than 100 million years).

Evidence of this enrichment process dates back to the 1970s, when scientists studying some mineral inclusions in meteorites concluded that they must have been pristine remains of the early solar system and contained the decay products of short-lived radionuclides. These radioactive elements may have been “blown” into the forming Solar System by a nearby supernova or by strong stellar winds emitted by a massive star known as the Wolf-Rayet star .

The authors of the new study, published Aug. 16 in Nature Astronomy , used multi-wavelength observations of the Ophiucus star-forming region – including spectacular new infrared data – to reveal interactions between gas clouds. star formation and the radionuclides produced in a nearby cluster of young stars . Their discovery indicates that supernovae in the star cluster are the most likely source of short-lived radionuclides in star-forming clouds.

“The Solar System most likely formed in a gigantic molecular cloud together with a young star cluster, and one or more supernova events generated by some massive stars belonging to the cluster contaminated the gas that transformed into the Sun and its planetary system, ”explains Douglas NC Lin , professor emeritus of astronomy and astrophysics at UC Santa Cruz . “Although this scenario has been suggested in the past, the strength of this paper is to use multi-wavelength observations and sophisticated statistical analysis to infer a quantitative measurement of the likelihood of the model.”

The data from gamma-ray space telescopes, explains  John Forbes , first author of the study and researcher at the Flatiron Institute’s Center for Computational Astrophysics , allow the detection of gamma rays emitted by the radionuclide aluminum-26, a radioactive isotope of aluminum whose half-life is equal to 720 thousand years. “These are challenging observations,” says the researcher. “We can only convincingly detect it in two star-forming regions, and the best data come from the Ofiuco complex.”

Multi-wavelength observations of the star-forming region in Ofiuco reveal interactions between star-forming gas clouds and radionuclides produced in a nearby cluster of young stars. The top image (a) shows the distribution of aluminum-26 in red, plotted by gamma-ray emissions. The central box represents the area covered in the lower left image (b), which shows the distribution of the protostars in the Ophiucus clouds as red points. The inset area is shown in the lower right image (c), a deep near infrared color composite image of the L1688 cloud, containing many well-known dense gas prestellar nuclei with discs and protostars. Credits: Forbes et al., Nature Astronomy 2021

The Ophiuchus cloud complex contains many dense protostellar nuclei in various stages of star formation and protoplanetary disk development , which represent the earliest stages in the formation of a planetary system. By combining imaging data at wavelengths ranging from millimeters to gamma rays, the researchers were able to visualize a flux of aluminum-26 from the nearby star cluster to the Ophiuchus star-forming region.. “The enrichment process we are seeing in Ophiuchus is consistent with what happened during the formation of the Solar System 5 billion years ago,” explains Forbes. “Once we saw this nice example of how the process could happen, we started trying to model the nearby star cluster that produced the radionuclides we see in gamma rays today.”

Forbes has developed a model that takes into account every massive star that may have existed in this region – including mass, age, and the likelihood of exploding as a supernova – and incorporates the potential returns of aluminum-26 from stellar winds and supernovae. . The model allowed him to determine the likelihood of different scenarios for aluminum-26 production observed today. “We now have enough information to say that there is a 59 percent chance that it is due to supernovae and a 68 percent chance that it is from multiple sources and not just a supernova,” continues Forbes. This type of statistical analysis assigns probabilities to scenarios that astronomers have been discussing for the past 50 years, Lin noted. “This is the new direction for astronomy to quantify likelihood,” he adds.

The new findings also show that the amount of short-lived radionuclides incorporated into newly formed star systems can vary widely. “Many new star systems will be born with abundances of aluminum-26 in line with our solar system, but the variation is enormous, several orders of magnitude,” says Forbes. “This is important for the early evolution of planetary systems, as aluminum-26 is the main source of initial warming. More aluminum-26 probably means drier planets. ‘

The infrared data, which allowed the team to peer through dusty clouds at the heart of the star-forming complex, was obtained by co-author João Alves of the University of Vienna , as part of the ESO’s Vision survey of nearby star nurseries carried out using the Vista telescope , Chile. “There is nothing special about Ofiuco as a star-forming region,” concludes Alves. “It’s just a typical configuration of gas and massive young stars, so our results should be representative of the enrichment of short-lived radioactive elements in the formation of stars and planets throughout the Milky Way .”

Featured image: Deep near infrared color composite image of the L1688 cloud in the Ophiuco star formation complex from the ESO Visions survey, where blue, green and red are mapped to the Nir J (1.2 μm), H (1.6 μm) and Ks bands (2.2 μm), respectively. Credits: João Alves / Eso Visions

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