How was our solar system born? Study finds new clues

A study of the Ophiuchus star-forming complex offered new insights into the conditions under which our own solar system was born.

The study results were published in the journal Nature Astronomy.

An active star formation region in the constellation Ophiuchus is giving astronomers new insights into the conditions in which our own solar system was born.

In particular, the study showed how our solar system may have been enriched with short-lived radioactive elements.

Evidence of this enrichment process dates back to the 1970s, when scientists studying certain mineral inclusions in meteorites concluded that they were pristine remnants of the infant solar system and contained the decomposition products of short-lived radionuclides.

These radioactive elements may have been released into the nascent solar system by a nearby exploding star (a supernova) or by the strong stellar winds of a type of massive star known as the Wolf-Rayet star.

The authors of the new study used multi-wavelength observations of the Ophiuchus star-forming region, 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 indicated that supernovae in star clusters are the most likely source of short-lived radionuclides in star-forming clouds.

“Our solar system was likely formed in a giant molecular cloud along with a young star cluster, and one or more supernova events from some massive stars in this cluster contaminated the sun-turned gas and its planetary system,” co-author said. 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 observations from multiple wavelengths and sophisticated statistical analysis to derive a quantitative measure of the model’s probability,” he added.

The first author, John Forbes of the Flatiron Institute’s Center for Computational Astrophysics, said data from space-based gamma-ray telescopes allows detection of the gamma rays emitted by the short-lived aluminum-26 radionuclide.

“These are challenging observations. We can only convincingly detect it in two star-forming regions, and the best data are from the Ophiuchus complex,” he said.

The Ophiuchus cloud complex contains many dense protostar nuclei at various stages of star formation and protoplanetary disk development, representing the earliest stages in the formation of a planetary system.

By combining image data at wavelengths ranging from millimeters to gamma rays, the researchers were able to visualize a flux of aluminum-26 from the star cluster near the Ophiuchus star-forming region.

“The enrichment process we’re seeing on Ophiuchus is consistent with what happened during the formation of the solar system 5 billion years ago,” Forbes said.

“As soon as we saw this beautiful example of how the process could happen, we started trying to model the nearby star cluster that produced the radionuclides we see today in gamma rays,” he added.

Forbes developed a model that considers every massive star that could have existed in this region, including its mass, age and probability of exploding as a supernova, and incorporates the potential aluminum-26 yields of stellar winds and supernovae.

The model allowed him to determine the probabilities of different scenarios for the production of aluminum-26 observed today.

“We now have enough information to say there’s a 59 percent chance it’s due to supernovae and a 68 percent chance it’s from multiple sources and not just a supernova,” Forbes said.

This type of statistical analysis assigns probabilities to scenarios astronomers have debated for the past 50 years, Lin noted.

“This is the new direction in astronomy, to quantify probability,” he added.

The new findings also showed that the amount of short-lived radionuclides incorporated into newly formed star systems can vary widely.

“Many new star systems will be born with an abundance of aluminum-26 in line 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 main source of early warming. More aluminum-26 probably means drier planets,” he added.

The infrared data, which allowed the team to observe through dusty clouds the heart of the star formation complex, was obtained by co-author João Alves at the University of Vienna as part of the European Southern Observatory’s VISION study of nearby star nurseries using VISTA telescope in Chile.

“There is nothing special about Ophiuchus as a star-forming region,” said 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 along the Milky Way,” he concluded.

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


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