Did you ever wonder why stars shine so bright in the sky? It is thanks to the huge amount of energy generated when small, light atomic nuclei are forced to stick together to create bigger, heavier nuclei. Nuclear fusion inside stars transformed some of the hydrogen and helium produced during the Big Bang into heavier atoms, for example, into the carbon and oxygen that make up our own bodies, and into all the other chemical elements that make up our world. These chemical elements are ejected by stellar winds and supernovae, with each of these astrophysical objects carrying its own special nuclear fingerprint. Stellar fingerprints made by nuclear reactions are observed in the form of different amounts of different elements by analysing the light that comes from stars and by measuring tiny stardust grains found in meteorites. We use computer codes that reproduce the effects of nuclear reactions inside stars to interpret these observations and investigate the origin of matter in the Universe and the formation of the Sun and its Solar System.
This research group is the successor of the RADIOSTAR ERC project. The webpage of the group can be found here.
– Important result:
Wehmeyer B., López, A. Y., Coté, B. et al: Inhomogeneous Enrichment of Radioactive Nuclei in the Galaxy: Deposition of Live 53Mn, 60Fe, 182Hf, and 244Pu into Deep-sea Archives. Surfing the Wave? The Astrophysical Journal, Volume 944, Issue 2, id.121, 16 pp. 2023
https://ui.adsabs.harvard.edu/abs/2023ApJ...944..121W/abstract
Radioactive nuclei reach Earth by surfing supernova blast waves
Live radioactive nuclei from stellar explosions that decay with timescales of about 1 to 20 million years have been found on Earth trapped inside deep-sea rocks. These nuclei are produced by nuclear reactions in different types of single and interacting stars. The three radioactive nuclei detected so far on Earth, manganese-53, iron-60, and plutonium-244 are made in three very different astrophysical objects: thermonuclear supernovae from exploding white dwarfs, core-collapse supernovae from massive stars, and neutron star mergers, respectively. Although these astrophysical explosion events are very different in their nature, the produced nuclei were detected in deep-sea rocks in layers of similar depth. As these rocks are sedimentary, they accumulate over time. This means that each layer represents accretion events that correspond to a certain age. Therefore, these nuclei must have arrived on Earth simultaneously about 2 million years ago, although they are of very different astrophysical origin.
To understand how these nuclei made it to Earth, we used computer models to simulate how they are distributed throughout the Milky Way Galaxy. We found that although they were made in very different astrophysical explosion events, core-collapse supernova shock waves are responsible for pushing these nuclei around in the interstellar medium: These shock fronts collect the nuclei from their astrophysical production sites, mix them, and propagate them throughout the interstellar medium. This can explain why they were found within the same, or similar, layers of the deep-sea rocks. We also predict that hafnium-182, a radioactive nucleus made in red giant stars not massive enough to die in supernova explosions, should also be found in such sediments at similar depths. Experiments in laboratories around the world are underway and will help to verify our discovery.
Credit: ESO/L. Calçada/M. Kornmesser