We know where the stars rich in gold come from

Over the past five years, hundreds of gold-rich stars have been detected by advanced telescopes around the world. New galaxy formation simulations, with the highest resolution in both time and mass, show that these stars formed more than 10 billion years ago in small galaxies that merged to create the Way milky.

Stars are thermonuclear forges that produce most of the elements that make up planets. Most elements heavier than iron, including precious metals such as gold and platinum, are produced by the fast neutron capture process (the process r). When they die, stars release the heavy elements they have created into interstellar space, which can then be incorporated into the next generation of objects.

Like planets, new stars incorporate heavy elements released by previous generations. By studying the chemical composition of stars, we should be able to deduce the type of environment in which the stars were formed. The mystery was when, where and how these stars formed in the history of the Milky Way. Until now, there was no theoretical framework to explain the observed chemical diversity.

Reconstructing the history of the Milky Way using a supercomputer

An international research team led by Yutaka Hirai, from Tōhoku University (Japan) and the University of Notre Dame (Indiana, USA), has tracked the formation of a virtual galaxy similar to the Milky Way from the Big Bang to the present day with a numerical simulation. This simulation has the highest time and mass resolutions to date, allowing the team to study the cycle of new materials released by old stars and absorbed by new ones. These results (free access on arXiv) were published on November 14 in the Monthly Notices of the Royal Astronomical Society.

Using the Aterui II supercomputer at the Center for Computational Astrophysics of the National Astronomical Observatory of Japan, the team successfully ran the simulation for several months, allowing for the first time to analyze star formation. rich in gold in the Milky Way.

Stellar gems produced in very old galaxies

The standard cosmology the researchers used predicts that the Milky Way grew through the accretion and merger of small galaxies, called progenitor galaxies. Simulation data revealed that some, but not all, of the progenitor galaxies contained large amounts of the heaviest elements. Each neutron star merger event—a confirmed site of heavy-element nucleosynthesis—has increased the abundance of the heavier elements in these smaller galaxies. According to research, most gold-rich stars formed more than 10 billion years ago in these progenitor galaxies. The predicted abundance of gold-enriched stars in the final Milky Way-sized galaxy matches what is actually observed today in our Galaxy.

Looking ahead, Hirai and his team plan to simulate the formation of the Milky Way and clarify the origins of individual stars using the new Fugaku supercomputer.

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