Milky Way Has Hundreds Of Gold-Rich Stars. New Study Reveals When, Where And How They Were Born

The study found that most gold-rich stars were formed in dwarf galaxies over 10 billion years ago.

Did you know that the Milky Way galaxy has hundreds of gold-rich stars? These are stars with an abundance of heavy elements beyond iron, and contain gold and platinum, the "jewellery store elements''. Now, researchers from the University of Notre Dame and Tohoku University have found when, where and how these gold stars were formed in the Milky Way. The study revealing the birthplace of gold-rich stars was recently published in the Monthly Notices of the Royal Astronomical Society. 

State-of-the-art telescopes across the world have discovered hundreds of gold-rich stars in the Milky Way. The mystery of when, where and how these stars were formed has now been solved. 

When were gold-rich stars formed?

According to the new study, most gold-rich stars formed in small progenitor galaxies of the Milky Way over 10 billion years ago. A galaxy which is supposed to be at the origin of a specific event is called a progenitor galaxy. The new study sheds light on the past of gold-rich stars for the first time.

The researchers used a numerical simulation to track the Milky Way's formation from the Big Bang to the present. This helped them reach the conclusion about the stars' past. 

According to a statement released by the Royal Astronomical Society the simulation has the highest time resolution yet achieved, which means it can precisely resolve the cycle of materials formed by stars in the Milky Way. 

The researchers used the ATERUI II supercomputer in the Centre for Computational Astrophysics at the National Astronomical Observatory of Japan to produce the simulation. The process took several months to complete. 

How were gold-rich stars formed?

Using the simulation, the researchers were able to analyse the formation of gold-rich stars in the Milky Way for the first time. The simulation used a standard cosmology which predicts that the Milky Way grows by the accretion and merging of small progenitor galaxies. These galaxies existed over 10 billion years ago, and contained large amounts of the heaviest elements. 

According to the study, each event of neutron star merger increased the abundance of the heaviest elements in these small galaxies. Neutron star mergers were a confirmed site of heavy element nucleosynthesis, which refers to the creation of new atomic nuclei, the centres of atoms that are made up of protons and neutrons. It is also defined as the cosmic formation of atoms more complex than the hydrogen atom. 

Where were gold-rich stars formed?

The gold-rich stars formed in the small galaxies where nucleosynthesis occurred. The predicted abundances of gold-rich stars can be compared with the observations of the stars today. 

In the statement, Yutaka Hirai, one of the researchers involved in the study, said the gold-rich stars today tell us the history of the Milky Way. The team found that most gold-rich stars were formed in dwarf galaxies over 10 billion years ago.

Hirai added that the ancient galaxies are the building blocks of the Milky Way.  

Hirai added that comparison with simulations and observations in the Milky Way opens a new avenue for extracting fossil records of stars.

The study findings mean many of the gold-rich stars seen today are fossil records of the Milky Way's formation over 100 billion years ago.