Physics Research Team Discovers Highest Europium Content Ever Observed in Stars (Planetary Science)

A physics research team led by TU Darmstadt has discovered the highest europium content ever observed in stars. The work of the EUROPIUM group around Professor Almudena Arcones, who has received a grant from the European Research Council, has now been published in “The Astrophysical Journal”. Co-author is Dr. Moritz Reichert (member of EUROPIUM), co-author Dr. Camilla Hansen from the Max Planck Institute for Astronomy in Heidelberg.

Europium is the key to understanding the formation of the heavy elements through the rapid neutron capture process, the so-called r-process. This is crucial both for the formation of half of the elements that are heavier than iron and for the entire occurrence of thorium and uranium in the universe. TheEUROPIUM group has combined theoretical astrophysical simulations with observations of the oldest stars in our galaxy and in dwarf galaxies. The latter are small, dark matter dominated galaxies that orbit our galaxy. Dwarf galaxies are excellent test objects for studying the r-process, as some of the oldest, metal-poor stars that have existed for 10 to 13 billion years have shown an abundance of r-process elements. Studies have even postulated that only a single neutron-rich event could be responsible for this accumulation in the smallest dwarf galaxies.

With their new discovery, the researchers in Darmstadt and Heidelberg have succeeded in determining the highest europium content ever observed – and they have coined a new name for these stars: “Europium stars”. These stars belong to the dwarf galaxy Fornax – a spheroid dwarf galaxy with a high star content. In their publication, the group also reports on the first ever observation of lutetium in a dwarf galaxy and the largest sample of observed zirconium.

A very rare find

The “Europium Stars” in Fornax were born shortly after an explosive production of heavy elements. Due to the high stellar metal abundance, the extreme r-process event must have occurred only four to five billion years ago. This is a very rare find as most europium-rich stars are much older. Therefore, the Europium stars give insights into the origin of the elements in the universe at a very specific and late point in time.

Heavy elements are created by the r-process when two neutron stars merge or when massive stars with strong magnetic fields are explosive. The EUROPIUM group analyzed these two high-energy events and carried out detailed studies on element production in these environments. However, due to the still great uncertainties in the nuclear physics information, it is not possible to clearly assign the heavy elements in the “europium stars” to one of this astro-physical environment. Future experiments in the new FAIR accelerator center at the GSI Helmholtz Center for Heavy Ion Research in Darmstadt will significantly reduce these uncertainties.

In addition, the new Hessian cluster project ELEMENTS, in which Professor Arcones is the lead researcher, combining in a unique way simulations of neutron star mergers , nucleosynthesis calculations with the latest experimental information and observations to investigate the longstanding question: Where and how are heavy elements produced in the universe?

Featured image: The EUROPIUM group has combined theoretical astrophysical simulations with observations of the oldest stars in our galaxy and in dwarf galaxies.

The publication

Extreme r-process Enhanced Stars at High Metallicity in Fornax

Provided by Technische Universitat Dramstadt

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