Was the Early Universe Carbon rich?
DFG-ANR Funding for French-German Research Project

An interdisciplinary research project between the Max Planck Institute for Astronomy in Heidelberg (MPIA) and the universities of Heidelberg and Montpellier (France) aims to solve a mystery that is currently occupying astrophysicists: Was the early universe carbon rich?  The German Research Foundation (DFG) and the French National Research Agency (ANR) are now providing a total of 900,000 Euros for this challenging project.

People often talk about a “golden age of astrophysics” these days. Indeed, research into the cosmos is currently experiencing a surge of discoveries, thereby spurring fundamental physics research. Modern ground- and space-based telescopes, such as James Webb and the Very Large Telescope, offer a completely new level of observational quality. Huge amounts of data from surveys such as Gaia and Euclid also allow for observations of billions of objects across vast astronomical scales. Together with modern methods of data science and theoretical simulations, new opportunities emerge through innovative combination of data and physical theory.

Millions of Stellar Spectra

A new era has also dawned in the field of large-scale spectroscopic studies in astronomy. Spectra are extremely important for astrophysics. The light, broken down into individual wavelengths, is like a fingerprint and reveals a multitude of physical properties of objects—including their chemical composition.

With 4MOST (4-meter Multi-Object Spectroscopic Telescope), located at ESO’s Paranal Observatory in Chile, a state-of-the-art facility is now available, which can simultaneously observe over 2,500 objects. The project, in which MPIA is also a key participant, will yield millions of high-quality spectra of stars in the Milky Way galaxy and its outskirts. This presents a unique opportunity to solve scientific mysteries whose answers depend on the identification of rare objects—in other words, on finding those “needles in a haystack” that have remained hidden until now.

One of these fundamental questions is: Was the early universe rich in carbon?
We don’t know the answer yet, but it is now set to be answered in the recently funded DFG-ANR project!

First generation of stars formed from carbon-rich dust?

The question mentioned above arises from the discovery of so-called CEMP stars—which are carbon-enriched but also metal-poor — some of which are considered direct descendants of the first generation of stars in the universe. CEMP stars are unexpectedly rich in carbon. Relative to iron, their carbon-over-iron ratio exceeds that of “normal stars” like our Sun by factors of 10 to 100, whereas other heavy elements are depleted by a factor 100s to 1000s.

However, how these stars came to have such extreme carbon enrichment remains (yet) unclear. It is possible that the earliest phases of the universe were rich in carbon-bearing dust—a scenario that aligns remarkably well with recent evidence from observations with the James Webb Space Telescope showing carbon enrichment and dust in high-redshift galaxies, and thus in the early epochs of the universe.

Perhaps efficient gas fragmentation associated with this dust favored the formation of low-mass (and long-lived) stars. If yes, this may lead to a substantial population of such first-generation, also called Population III, low-mass stars in the Milky Way.

“Using new high-resolution 4MOST spectra, we will determine the carbon abundances of over 50,000 extremely metal-poor star candidates in the Galactic disk and bulge. These measurements will be compared with models of Population III star formation, which will provide new insights into the properties of the Milky Way’s earliest stellar generations,” says Maria Bergemann, independent Lise Meitner Group Leader at MPIA, who heads the Stellar Spectroscopy and Stellar Populations research group. “Our goal is to critically test the CEMP findings: Are low-metallicity stars actually carbon-enriched, as observations suggest? All observational studies to date have relied on highly simplified 1D-LTE (local thermodynamic equilibrium) models for carbon diagnostics, but verification of whether this assumption is valid is still pending.”

Funding for an Interdisciplinary German-French Project

Together with partners at the Universities of Montpellier and Heidelberg, this question will now be addressed as part of a highly interdisciplinary program. The project will combine methods from molecular quantum mechanics, machine learning, the application of stellar models (particularly those of Pop III star formation), and observational spectroscopy.

The project will establish molecular stellar diagnostics as a powerful new approach for mapping stellar nucleosynthesis, studying the chemical enrichment of the Milky Way, and uncovering the origin and evolution of the earliest generations of stars.

For this challenge, a collaboration between the groups led by Simon Glover (University of Heidelberg), Bertrand Plez and Yohann Scribano (University of Montpellier, LUPM), and  Maria Bergemann (MPIA) is planned.

The total funding amounts to approximately 900,000 Euros, of which about half a million goes to the project partners in Germany. Maria Bergemann is receiving funding for a postdoctoral position, and a total of approximately 353,000 Euros is going to the MPIA.

ANR-DFG French-German Collaboration for Joint Projects in Natural, Life and Engineering Sciences 

 

KJ/MB