Seeking the First Generation of Stars
The first stars in the universe collapsed into being in clouds of pristine gas containing just hydrogen, helium, and a tiny amount of lithium. This simple set of chemical ingredients likely allowed the first generation of stars to attain enormous masses, although the exact distribution of their masses is unknown. These early stars created new elements in their cores and scattered them throughout the universe in expansive clouds of metal-enriched gas.
While massive stars from this first generation are long gone from the Milky Way, their descendants may still roam the galaxy. Finding these descendants - especially those that can trace their material back to a single member of the first generation - would provide a powerful way to study the first stars in the universe. Recently, researchers claimed to have found such a star, called J1010+2358.
The star's overall lack of metals (elements heavier than helium, in astronomer parlance) and curious chemical abundance pattern suggest that it was made from gas left behind by a 260-solar-mass star; J1010+2358 is especially lacking in elements with odd atomic numbers, such as sodium, compared to even-numbered elements. Now, a team led by Ioanna Koutsouridou (University of Florence) has investigated whether J1010+2358 is truly the descendant of a single, massive member of the first generation of stars.
A Study in Stellar Genealogy
Koutsouridou's team examined whether J1010+2358 contains material passed down from only a single 260-solar-mass star, or if it contains material from several stars. Using chemical abundance modeling, the team found that J1010+2358 must have descended from a 260-solar-mass star - but it could have other stellar parents as well. In fact, without being able to measure several critical chemical elements in J1010+2358's spectrum, it's only possible to say that the reported stellar ancestor contributed at least 10% of J1010+2358's metals.
While J1010+2358 may have more than one stellar parent, its properties can still help researchers probe the generation of stars that came before it. Using models of how the Milky Way's chemical enrichment evolved over time, Koutsouridou and collaborators used the non-detection of stars enriched by just one first-star ancestor to constrain the masses of the first stars. The strength of the constraint depends on how much of J1010+2358's material came from its 260-solar-mass ancestor; only if more than 70% of the star's metals came from a single ancestor can its chemical abundance pattern constrain the possible mass distribution of the first stars.
The hunt for descendants of the first stars goes on: high-resolution surveys continue to dredge up stars with just one first-generation stellar ancestor, and future observations may fill in the missing elemental abundance measurements in J1010+2358's spectrum and clarify its family tree.
Research Report:True Pair-instability Supernova Descendant: Implications for the First Stars' Mass Distribution
Related Links
AAS Nova
Stellar Chemistry, The Universe And All Within It
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