RADIOSTAR will exploit radioactive nuclei produced by nuclear reactions inside stars and ejected by stellar winds and supernova explosions to fill the missing pieces of the puzzle of the origin of our Solar System: What were the circumstances of the birth of our Sun? Were they similar to those of the majority of other stars in our Galaxy, or were they special? Radioactive nuclei are the key to answer these questions because meteoritic analysis has proven that many of them were present at the time of the birth of the Sun. Their origin, however, has been so far elusive. RADIOSTAR steps beyond the state-of-the-art to answer these open questions by (i) combining the evolution of radioactive nuclei in the Galaxy and within molecular clouds and (ii) considering all the seventeen radionuclides of interest and all their stellar sources and analysing the effects of uncertainties in their stellar production. This will allow us to: - Use the decay of radioactive nuclei produced by the chemical evolution of the Galaxy as a clock to measure the lifetime of the Sun’s parent molecular cloud prior to the Sun’s birth; - Calculate the self-pollution of this molecular cloud from the ejecta of stars with lives shorter than such lifetime; - Discover if such self-pollution can fully explain the abundances of radioactive nuclei present at the time of the birth of the Sun, or whether special conditions are required. RADIOSTAR will also have a far-reaching impact on our understanding of exoplanetary systems because the heat produced by radioactivity affects the evolution of planetesimals, with implications for the amount of water on terrestrial planets in the habitable zone. RADIOSTAR will open a new window into research on the effect of radioactivity on the evolution of planetesimals outside our Solar System.

In this ERC Starting Grant, I propose an ambitious research program to target important challenges in predicting realistic initial conditions for the planet formation process. I will perform a large systematic study of the accretion-driven eruptions of newborn stars, and evaluate their influence on the structure, composition, and chemistry of the terrestrial planet forming zone in the circumstellar disk. The research will focus on three main questions: - How does the mass accretion proceed in realistic, structured, non-axisymmetric disks? - What physical mechanisms explain the accretion-driven eruptions? - What is the effect of the eruptions on the disk? My new research group will study young eruptive stars, pre-main sequence objects prone to episodes of extremely powerful accretion-driven outbursts, and combine new observations, state-of-the-art numerical modelling, and information from the literature. With a novel concept, we will first model the time-dependence of mass accretion in circumstellar disks, taking into account the latest observational results on inhomogeneous disk structure, and determine what fraction of young stellar objects is susceptible to high mass accretion peaks. Next, we will revise the paradigm of the eruptive phenomenon, compelled by recently discovered young eruptive stars whose outbursts are inconsistent with current outburst theories. Finally, we will determine the impact of accretion-driven eruptions on the disk, by considering the increased external irradiation, internal accretion heating, and stellar winds. With my experience and track record, I am in a position to comprehensively synthesize existing and newly acquired information to reach the proposed goals. The expected outcome of the ERC project is a conclusive demonstration of the ubiquity and profound impact of episodic accretion on disk structure, providing the initial physical conditions for disk evolution and planet formation models.

To understand our cosmic origins requires understanding the formation of the Galaxy, which in turn requires precise characterization of its fundamental building blocks: stars. The essential nature of this knowledge has driven the Gaia and TESS space telescope missions, but to take full advantage of this, our estimates of non-observable stellar properties must improve at pace. The proposed project uses the unprecedented data volume and accuracy from Gaia and TESS and the Experienced Researcher (ER), Dr Joyce’s knowledge of multiple theoretical dating techniques to derive the best ages possible for stars in the Milky Way. The ER will use stellar structure and evolution models, stellar oscillation programs, isochrones, and novel data science techniques to provide ages for oscillating binaries, metal-poor stars, Gaia benchmark stars, and exotic variables across the mass spectrum. Whereas most stellar modelers specialize in particular stars, the ER is unique in the breadth of her repertoire. Dr. Joyce’s theoretical expertise is the ideal complement to the world-class observers at Konkoly Observatory, whose interests also span a wide range of stellar types. Her supervisor and long-time collaborator, Dr László Molnár, is an expert in stellar variability, member of the TESS and Gaia consortia, and recently tenured academic at Konkoly Observatory, CSFK, an institution with which the ER has long-standing rapport and many other collaborators. The supervisor of her secondment at KU Leuven, Prof. Conny Aerts, is one of the founders and world leaders of the field of asteroseismology. The ER’s role on the development team of the widely used, open-source Modules for Experiments in Stellar Astrophysics (MESA) program will allow her to build broadly applicable and freely disseminated tools with high efficiency. In return, Konkoly Observatory will benefit strongly from the presence of a MESA developer, thus facilitating the transfer of theoretical knowledge as well as technical skill.

The proposed project is a crossroad of noble gas cosmochemistry, geochemical modelling and astrophysics. We will obtain a best estimate of the initial 244 Plutonium content of the Solar System at the time when the first condensed mineral assemblages formed in the hot solar nebula. We will apply this value to model the volatile depletion history of the silicate Earth and to produce the first self-consistent estimate on the timing of the last addition of matter produced in rapid neutron capture processes (r process) to the Solar System. 244 Pu is an r-process- only short lived radionuclide that goes through spontaneous fission to produce Xenon isotopes and in principle the 244 Pu-Xe system can be used as chronometer to date early volatile loss events in Solar System solids. We propose a comprehensive experimental approach to study noble gases in combination with Nd (similarly volatile to Pu) and U (more volatile than Pu) abundances on a complementary set of samples that is adequate to explain the possible variation in the initial Pu/U ratio in different meteorites and early condensed mineral assemblages and to evaluate the applicability of the chronometer. While the Experienced Researcher is an expert in noble gas geochemistry and has experience in geochemical modelling, she will gain the knowledge on cosmochemistry and stellar nucleosynthesis required to interpret and discuss the new results produced in this project. The individual fellowship will help her start her early career as a postdoc and provide a crucial mobility to build a network in Europe and do research with high impact.

The consensus ΛCDM (Lambda-Cold Dark Matter) model of cosmology has shown remarkable explanatory power over a variety of cosmic scales and epochs, and it narrates a reassuring story of a universe currently filled mostly with dark matter and dark energy. Yet, this explanation is not fully satisfactory because the actual nature of the dark components remains a puzzle. Furthermore, cosmologists have recently reported significant anomalies concerning the delicate balance of cosmic expansion and structure growth, without a compelling solution. The main objective of the MAPEX project is to reassess this far-reaching problem from a new perspective, and determine if cosmological tensions can be traced to the most extreme cosmic web environments: deep voids and dense superclusters. This EU-funded action will allow me to access unprecedented new data taken at the Vera Rubin Observatory, solidifying and broadening the Hungarian contributions to the next-generation Legacy Survey of Space and Time (LSST) project based in Chile. To go beyond the state-of-the-art, I will acquire extensive skills on machine learning techniques from expert researchers at Konkoly Observatory to combine with my groundwork results on cosmological data analysis from, above all, the Dark Energy Survey (DES). As a key innovation, I will develop deep learning models to study extreme voids and superclusters. First, I will apply convolutional neural network methods to augment traditional cross-correlations between galaxy density fluctuations and the anisotropies of the Cosmic Microwave Background. Then, I will capture the dependence of their gravitational signals on the physical properties of dark energy and dark matter. The proposed analyses of simulations and early observational LSST data will help resolve whether some as-yet unknown physical effects or systematic biases complicate the picture in cosmology. Either way we will gather fundamentally new knowledge about the Universe on the largest scales.