BRIdging Disciplines of Galactic Chemical Evolution (BRIDGCE) Consortium 2021-2024

"How did the Universe begin and evolve" is one of the three science challenges identified in the STFC Astronomy Programme. We address this question by modelling physical processes from the micro (nuclear, stellar) to the macro scales (galactic, cosmological), studying the ionising and chemical feedback from stars and the wider context of galaxy formation.

The BRIDGCE consortium is a multidisciplinary collaboration between nuclear, stellar and extra-galactic astrophysicists, which aims to achieve a comprehensive understanding of the evolution of the Universe from the era of reionisation up to now, using chemical elements as fingerprints of the physical processes that occur in stars and galaxies. Elements heavier than helium are produced in stars and supernovae on different timescales, and the stellar populations and interstellar medium within galaxies keep a record of star formation and chemical enrichment histories of galaxies.

Therefore, it is also possible to constrain galaxy formation theory from the observed elemental abundances, and to do this more accurately we need to understand stellar and nuclear Astrophysics. Moreover, the discovery of gravitational waves (GW) has opened a new window to the Universe, allowing us to observe the formation of black holes and neutron stars more directly than ever before.

GWs can provide independent new constraints on stellar winds, evolution, and stellar deaths via black hole remnants, and the seeds of super-massive black holes in galaxies.

The development of high-performance computing enables us to study the theory of stars and galaxies self-consistently: we simulate how stars lose mass via stellar winds prior to supernovae explosions (Project-1); we simulate the full evolution of stars in one-dimension (1D) and compute 3D scans of their interiors (Project-2). Furthermore, by combining stellar evolution and nucleosynthesis to galactic dynamical evolution, we reproduce the entire chemodynamical history of local dwarf galaxies (Project-3) and of the Milky Way (Project-4).

Our research addresses some of the key questions of 21st century Astronomy: How black holes and neutron stars are formed (Projects 1 & 2)?, How many GW events will be detected in future missions?, and How we can trace the evolution of the Universe from GWs (Project-5)?

Nuclear data (nuclear reaction rates in particular) are a key input for stellar evolution models since nuclear reactions provide the energy that powers stars. This information determines stellar lifetimes and the composition of their ejecta. Stars provide important feedback into galaxies through the light they radiate, their powerful winds and explosions, and all the chemical elements they produce.

The outputs of stellar models are thus key ingredients for galactic chemical evolution models. These models follow successive episodes of star formation and trace the history of the enrichment of the elements. The model predictions can then be compared to observations of stars, stellar populations, and the inter-stellar medium that carries the chemical fingerprints of the cumulative chemical enrichment that preceded their birth.

Comparison to observations can thus constrain both the galactic and stellar properties. Finally, most stars are not born on their own, but may instead evolve interacting with a companion. Although this has been known for decades, the impact of binarity on galaxy evolution is poorly known.

In the BRIDGCE 2021-2024 grant, our galaxy experts will explore this new scientific problem together with our stellar experts. Our consortium project applies innovative techniques across different disciplines and tackles this challenge through 5 projects corresponding to very different physical scales: stellar envelopes (Project-1), stellar cores (Project-2), local dwarf galaxies (Project-3), the Milky Way (Project-4), and the Universe as a whole (Project-5). These impact many areas of Astrophysics as well as Cosmology & Nuclear Physics.