Exceptional stars: the universe’s most pristine objects.

A star relatively close to us appears to be almost devoid of heavy elements produced by supernovae and may be a direct descendant of the universe’s first star.

Astronomers postulate that the initial stars consisted solely of hydrogen and helium, remnants from the Big Bang. It was only after these stars exhausted their fuel and exploded as supernovae that heavier elements could disperse beyond helium. The gas enriched with these new elements formed the subsequent generation of stars, with this cycle continuing, ultimately producing the elements we see in today’s stars and planets.

Most stars observed in our galaxy belong to multiple generations and are excluded from this early star population. However, “star archaeologists” have discovered nearly untouched stars believed to be from the “second generation,” born from the remnants of the early stellar explosions.

Recently, Alexander Z from the University of Chicago and his team identified the star with the lowest total amount of “metals,” referring to all elements besides hydrogen or helium, in the known universe. Named SDSS J0715-7334, this star resides in the Large Magellanic Cloud, a satellite galaxy of the Milky Way, and has a metal content approximately 0.8 times that of our Sun, making it about 20,000 times less metallic.

After initially detecting the star in data from the Sloan Digital Sky Survey, due to its notably low metallicity, JI and his colleagues conducted observations with the Magellan telescope at the Las Campanas Observatory in Chile. They confirmed that while the star has minimal iron, comparable to other nearly untouched stars, it also exhibits very low carbon levels, which are not typical for Milky Way stars.

“It’s quite an exciting discovery regarding iron levels. This is even more extreme than some of the other examples we have previously found,” said Anke Ardern-Arentsen from Cambridge University. “However, most interestingly, this star has significantly less carbon compared to natural stars we know about.” This observation might imply that it formed in a distinctly different manner than stars found in the Milky Way, according to Anna Frebel from MIT.

To form a star like SDSS J0715-7334, a relatively small and cool gas mass is required. Typically, this process necessitates heavier elements with high-energy electrons, such as carbon, which aid in cooling the gas effectively. The scarcity of carbon in this star complicates this process.

One potential alternative explanation is the presence of a cloud of cosmic dust made up of heavier elements. This dust may contribute to cooling, a mechanism not observed early in the universe’s history, at least within our own galaxies.

“There’s an issue here. Do varying environments across different regions of the universe cool gas at different rates during the early formation epochs?” Frebel questions. “We can raise the question of why different cooling rates occur, but we lack a satisfactory answer.”

World Capital of Astronomy: Chile

Discover the astronomical wonders of Chile. Visit some of the globe’s most advanced observatories and gaze upon the stars in one of the clearest night skies on Earth.