Differences Observed In Giant Binary Stellar Systems

Eddie Gonzales Jr. – MessageToEagle.com – Astronomers utilizing the Gemini South telescope have confirmed that differences in the composition of binary star systems can originate from chemical variances within the nebulous cloud of stellar material from which they originated.

These findings contribute to explaining why stars born from the same molecular cloud can exhibit different chemical compositions and harbor different planetary systems. They also pose challenges to prevailing models of stellar and planetary formation.

Up to 85% of stars are estimated to exist in binary star systems, with some even residing in systems comprising three or more stellar bodies. These stellar pairs emerge from the same molecular cloud, sharing abundant chemical building blocks. Consequently, astronomers would anticipate finding that they possess nearly identical compositions and planetary systems.

Numerous binary systems, however, deviate from this pattern.

Although some proposed explanations attribute these differences to events occurring after the stellar evolution process, astronomers have definitely confirmed for the first time that such dissimilarities originate from the pre-formation stage when the stars began to form.

The team, led by Carlos Saffe from the Institute of Astronomical, Earth, and Space Sciences (ICATE-CONICET) in Argentina, used the Gemini High-Resolution Optical Spectrograph (GHOST), which is renowned for its precision.

The researchers conducted an analysis of the diverse wavelengths of light, or spectra, emitted by a binary system comprising two massive stellar bodies. This examination unveiled substantial disparities in their respective chemical compositions.

“GHOST’s extremely high-quality spectra offered unprecedented resolution,” said Saffe. “Itallowed us to measure the stars’ stellar parameters and chemical abundances with the highest possible precision.”

Previous studies have proposed three possible explanations for observed chemical differences between binary stars. Two of them involve processes that would occur well into the stars’ evolution: atomic diffusion, or the settling of chemical elements into gradient layers depending on each star’s temperature and surface gravity, and the engulfment of a small, rocky planet, which would introduce chemical variations in a star’s composition.

The third possible explanation looks back at the beginning of the stars’ formation, suggesting that the differences originate from primordial or pre-existing areas of nonuniformity within the molecular cloud. In simpler terms, if the molecular cloud has an uneven distribution of chemical elements, then stars born within that cloud will have different compositions depending on which elements were available at the location where each formed.

So far, studies have concluded that all three explanations are probable; however, these studies focused solely on main sequence binaries. The ‘main sequence’ is the stage where a star spends most of its existence, and the majority of stars in the universe are main-sequence stars, including our sun.

Instead, Saffe and his team observed a binary consisting of two giant stars. These stars possess extremely deep and strongly turbulent external layers or convective zones. Owing to the properties of these thick convective zones, the team was able to rule out two of the three possible explanations.

The continuous swirling of fluid within the convective zone would make it difficult for the material to settle into layers, meaning giant stars are less sensitive to the effects of atomic diffusion—ruling out the first explanation. The thick external layer also means that a planetary engulfment would not change a star’s composition much since the ingested material would rapidly be diluted—ruling out the second explanation.

This leaves primordial inhomogeneities within the molecular cloud as the confirmed explanation. “This is the first time astronomers have confirmed that differences between binary stars begin at the earliest stages of their formation,” said Saffe.

“Using the precision-measurement capabilities provided by the GHOST instrument, Gemini South is now collecting observations of stars at the end of their lives to reveal the environment in which they were born,” says Martin Still, NSF program director for the International Gemini Observatory.

“This allows us to explore how the conditions in which stars form can influence their entire existence over millions or billions of years.”

Three consequences of this study are of particular significance. First, these results explain why astronomers see binary stars with such different planetary systems. “Different planetary systems could mean very different planets—rocky, Earth-like, ice giants, gas giants—that orbit their host stars at different distances and where the potential to support life might be very different,” said Saffe.

Second, these results pose a crucial challenge to the concept of chemical tagging—using chemical composition to identify stars that came from the same environment or stellar nursery—by showing that stars with different chemical compositions can still have the same origin.

Paper

Written by Eddie Gonzales  Jr. – MessageToEagle.com Staff Writer