Gold-rich stars: A gold-colored spiral galaxy.

terrestrial sky | Gold-rich stars as “fossils” of the Milky Way

Simulated Milky Way-like galaxy at the present time, taken from the simulation created while studying gold-rich stars. Simulation: Takayuki Saitoh (Kobe University/Tokyo Tech ELSI). Visualization: Takaaki Takeda (VASA Entertainment Co. Ltd.). Image via the Royal Astronomical Society (CC BY 4.0).

Gold is formed in supernovae and neutron star collisions

Where does gold come from? It comes from the earth, of course, but it’s the gold of the earth developed in space. It is produced in supernovae (exploding stars) and in neutron star collisions in a series of nuclear reactions known to scientists as the r-process. Astronomers using state-of-the-art telescopes have discovered hundreds of gold-rich stars in our Milky Way. But they wanted to understand when, where and how these stars formed. On November 14, 2022, the London-based Royal Astronomical Society announced a new numerical simulation showing that most of the gold-rich stars formed in low-mass dwarf galaxies that merged with our Milky Way about 10 billion years ago.

They said this new work is the first to shed light on these stars’ pasts. And they pointed out that gold-rich stars form a “fossil record,” giving astronomers a new tool for studying our galaxy’s history.

The scientists conducting the study are from the University of Notre Dame and Tohoku University. The research appears in the peer-reviewed scientific journal Monthly Bulletins of the Royal Astronomical Society.

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On the trail of the history of the Milky Way

These astronomers use the term “gold-rich” to describe stars that contain large amounts of heavy elements (other than iron), including the so-called “jeweling elements,” gold and platinum.

They used the supercomputer ATERUI II at the Center for Computational Science at the National Astronomical Observatory of Japan to create their numerical simulation. They said it traces the formation of the Milky Way from the Big Bang to the present day with a high level of detail time. Said:

This simulation has the highest temporal resolution to date: It can precisely resolve the material cycle of the stars in the Milky Way…

Standard cosmology used predicts that the Milky Way grows through the accretion and merger of small progenitor galaxies [the small galaxies that merged with our Milky Way to create the large galaxy we live in today].

Gold-rich stars as “fossils”

The simulation data showed that some of the progenitor galaxies – which existed over 10 billion years ago – contained large amounts of the heaviest elements. These heavy elements came from neutron star mergers, they said, a known source of heavy element formation. Said:

The gold-rich stars formed in these galaxies and their predicted abundance can be compared to observations of present-day stars.

Yutaka Hirai from Tohoku University commented:

The gold-rich stars tell us the history of the Milky Way today. We found that most gold-rich stars formed in dwarf galaxies over 10 billion years ago. These ancient galaxies are the building blocks of the Milky Way.

Our results mean that many of the gold-rich stars we see today are the fossil record of the formation of the Milky Way more than 10 billion years ago.

And he added:

Comparison with simulations and observations in the Milky Way opens a new way to extract the fossil record of stars.

Conclusion: New computer simulations show that most of the gold-rich stars formed in low-mass dwarf galaxies that merged with our Milky Way about 10 billion years ago.

Source: Neutron star mergers as an astrophysical location of the r-process in the Milky Way and its companion galaxies

About the Royal Astronomical Society

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