New radioactive clues to the formation of our solar system from the nearby stellar nursery

Multi-wavelength observations of the star-forming region of Ophiuchus reveal interactions between clouds of star-forming gas 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 protostars in Ophiuchus clouds as red dots. The area in the box is shown in the lower right image (c), a deep near infrared color composite image of the L1688 cloud, containing many well-known prestellar dense gas nuclei with disks and protostars. Credit: Forbes et al., Nature Astronomy 2021

The Ophiuchus star formation complex offers an analogue for the formation of the solar system, including sources of elements found in early meteorites.

A region of active star formation in the constellation Ophiuchus gives astronomers new insights into the conditions under which our own solar system was born. In particular, a new study of the Ophiuchus star formation complex shows how our solar system may have become enriched with short-lived radioactive elements.

Evidence for this enrichment process has existed since the 1970s, when scientists studying certain mineral inclusions in meteorites concluded that they were primitive remnants of the nascent solar system and contained the decay products of radionuclides. short-lived. These radioactive elements could have been blown into the nascent Solar System by a nearby exploding star (a supernova) or by strong stellar winds from a type of massive star known as the Wolf-Rayet star.

The authors of the new study, published today (August 16, 2021) in Nature astronomy, used multi-wavelength observations of the star-forming region of Ophiuchus, including spectacular new infrared data, to reveal the interactions between star-forming gas clouds and radionuclides produced in a nearby cluster of young stars. Their findings indicate that supernovas in the star cluster are the most likely source of short-lived radionuclides in stellar clouds.

“Our solar system most likely formed in a giant molecular cloud with a young star cluster, and one or more supernova events from some massive stars in this cluster contaminated the gas that turned into the sun and its planetary system. said co-author 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 that it uses multi-wavelength observations and sophisticated statistical analysis to derive a quantitative measure of the model’s likelihood.”


Deep near infrared color composite image of cloud L1688 in the Ophiuchus star formation complex of the VISIONS European Southern Observatory public inquiry, where blue, green and red are mapped to the NIR J bands (1.2 m) , H (1.6 m) and KS (2.2 µm), respectively. Credit: João Alves / ESO VISIONS

First author John Forbes, of the Flatiron Institute’s Center for Computational Astrophysics, said data from space-based gamma-ray telescopes allows detection of gamma rays emitted by the short-lived radionuclide aluminum-26. “These are difficult observations. We can only convincingly detect it in two regions of star formation, and the best data comes from the Ophiuchus complex, ”he said.

The Ophiuchus cloud complex contains many dense protostellar nuclei at various stages of star formation and protoplanetary disc development, representing the early stages in the formation of a planetary system. By combining imaging data in 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 star-forming region of Ophiuchus.

“The enrichment process that we are observing at Ophiuchus is consistent with what happened during the formation of the solar system 5 billion years ago,” said Forbes. “Once we saw this beautiful example of how the process could happen, we tried to model the nearby star cluster that produced the radionuclides we see in gamma rays today.”

Forbes developed a model that takes into account every massive star that might have existed in this region, including its mass, age, and likelihood of exploding as a supernova, and incorporates the potential aluminum-26 returns from the winds. stellars and supernovas. The model allowed him to determine the probabilities of different aluminum-26 production scenarios observed today.

“We now have enough information to say that there is a 59% chance that it is due to supernovas and 68% chance that it is from multiple sources and not just one supernova,” Forbes said.

This type of statistical analysis assigns probabilities to scenarios that astronomers have debated for 50 years, Lin noted. “This is the new direction of astronomy, to quantify probability,” he said.

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 consistent with our solar system, but the variation is huge – several orders of magnitude,” Forbes said. “This is important for the early evolution of planetary systems, as aluminum-26 is the primary source of early heat. More aluminum-26 probably means drier planets.

The infrared data, which allowed the team to peer through the 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 VISION survey of the European Southern Observatory on nearby stellar nurseries using VISTA. telescope in Chile.

“There is nothing special about Ophiuchus as a region of star formation,” Alves said. “This is 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 across the globe. Milky Way. “

Reference: “A Solar System formation analog in the Ophiuchus star-forming complex” August 16, 2021, Nature astronomy.
DOI: 10.1038 / s41550-021-01442-9

The team also used data from the European Space Agency’s (ESA) Herschel Space Observatory, ESA’s Planck satellite and ">NasaCompton Gamma Ray Observatory.

Arline J. Mercier

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