Johnson, and 16 co-authors, reported in mid-2020 that the problem of the origin of the elements is a fundamental one in astronomy and one that has many open questions. Prominent examples include:
1) the nature of Type Ia supernovae and the timescale of their contributions;
2) the observational identification of elements such as titanium and potassium with the α-elements in conflict with core-collapse supernova predictions;
3) the number and relative importance of r-process sites;
4) the origin of carbon and nitrogen and the influence of mixing and mass loss in winds; and
5) the origin of the intermediate elements, such as Cu, Ge, As, and Se, that bridge the region between charged-particle and neutron-capture reactions.
The next decade will bring to maturity many of the new tools that have recently made their mark, such as large-scale chemical cartography of the Milky Way and its satellites, the addition of astrometric and asteroseismic information, the detection and characterization of gravitational wave events, 3-D simulations of convection and model atmospheres, and improved laboratory measurements for transition probabilities and nuclear masses. All of these areas are key for continued improvement, and such improvement will benefit many areas of astrophysics.
The origin of the elements remains one of the great problems in astrophysics and nuclear physics. We understand some basic components of the story, such as the origin of α-elements in core-collapse supernovae (CCSN) and the contribution of both CCSN and Type Ia supernovae (SNIa) to iron-peak elements. However, our understanding of many other elements is more uncertain, and we have only limited knowledge of where and when the elements in present-day Milky Way stars were formed and of how many metals of different species were ejected from the Galaxy rather than incorporated into stars.
The elemental abundances of stars and the Interstellar Medium (ISM), in the Milky Way and other galaxies, are sensitively tied to many other areas of
astrophysics: the physics of all varieties of supernovae; rotation and internal mixing in massive stars and intermediate mass stars; binary stellar evolution; the stellar initial mass function and its variation with metallicity, time, or environment; black-hole formation; neutron-star mergers; the assembly and star formation history of the Milky Way; the physics of galaxy formation, star formation, and feedback; the formation and composition of planets.
The study of galactic chemical evolution has made dramatic strides over the past decade thanks largely to massive spectroscopic surveys that measure abundances and in some cases detailed chemical fingerprints of ∼ 105 stars. These surveys have demanded radical advances in analysis techniques, and they have been complemented by asteroseismology from Kepler, parallaxes and proper motions from Gaia, IFU abundance maps of thousands of low red-shift galaxies, measurements of gas content and metallicity evolution out to z = 4, and high-resolution spectroscopy of growing samples of selected stellar populations (low metallicity, solar twins, dwarf satellites and streams) from large telescopes.
The 2020s should see big advances on all of these fronts and an influx of critical new information from time-domain surveys (probing supernova progenitors and black hole formation) and from gravitational wave discoveries.
See the Periodic Table developed by Johnson and her team: https://i2mconsultants.com/downloads/corp/periodic_table_small_v3.pdf
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