Free Astronomy Magazine July-August 2024

40 JULY-AUGUST 2024 ASTRO PUBLISHING planet, which would introduce chemical variations in a star’s composition. The third possible expla- nation 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 molecu- lar cloud has an un- even distribution of chemical elements, then stars born within that cloud will have different compositions de- pending on which elements were avail- able at the location where each formed. So far, studies have concluded that all three explanations are probable; however, these stud- ies 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-se- quence stars, including our Sun. In- stead, Saffe and his team observed a binary consisting of two giant stars. These stars possess extremely deep and strongly turbulent exter- nal 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 material to set- tle into layers, meaning giant stars are less sensitive to the effects of atomic diffusion — ruling out the Observatory. “This gives us the ability to explore how the conditions in which stars form can influ- ence their entire ex- istence over millions or billions of years.” Three consequences of this study are of particular signifi- cance. First, these results offer an ex- planation for why astronomers see bi- nary stars with such different planetary systems. “Different planetary systems could mean very dif- ferent 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 differ- ent chemical compositions can still have the same origin. Finally, observed differences previ- ously attributed to planetary im- pacts on a star’s surface will need to be reviewed, as they might now be seen as having been there from the very beginning of the star’s life. “By showing for the first time that pri- mordial differences really are pres- ent and responsible for differences between twin stars, we show that star and planet formation could be more complex than initially thought,” said Saffe. “The Universe loves diversity!” T he colorful band of the Milky Way is poised above the 8.1-meter Gemini South telescope of NSF’s National Optical-Infrared Astronomy Research Laboratory in this arresting image, which depicts bright patches of stars threaded through with winding lanes of dust. The Galactic Center hangs di- rectly above the telescope, framing one of the most powerful astronomical observatories in the southern hemisphere. [International Gemini Observa- tory/NSF’s NOIRLab/AURA/Kwon O Chul] 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 ex- planation. This leaves primordial in- homogeneities within the molecular cloud as the confirmed explanation. “This is the first time astronomers have been able to confirm that dif- ferences between binary stars begin at the earliest stages of their forma- tion,” said Saffe. “Using the precision-measurement capabilities provided by the GHOST instrument, Gemini South is now col- lecting observations of stars at the end of their lives to reveal the envi- ronment in which they were born,” says Martin Still, NSF program di- rector for the International Gemini !