Catching Element Formation In The Act


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Contact: F.X.Timmes
my one page vitae,
full vitae,
research statement, and
teaching statement.
The Case for a New MeV Gamma-Ray Mission: Radionuclide Astronomy in the 2020s

A White Paper for the 2020 Decadal Survey

C.L. Fryer, F.X. Timmes, A, Hungerford, A. Couture, and 256 co-authors

Gamma-ray astronomy explores the most energetic photons in nature to address some of the most pressing puzzles in contemporary astrophysics. It encompasses a wide range of objects and phenomena: stars, supernovae, novae, neutron stars, stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays and relativistic-particle acceleration, and the evolution of galaxies. MeV γ-rays provide a unique probe of nuclear processes in astronomy, directly measuring radioactive decay, nuclear de-excitation, and positron annihilation. The substantial information carried by γ-ray photons allows us to see deeper into these objects, the bulk of the power is often emitted at $gamma;-ray energies, and radioactivity provides a natural physical clock that adds unique information.

New science will be driven by time-domain population studies at γ-ray energies. This science is enabled by next-generation γ-ray instruments with one to two orders of magnitude better sensitivity, larger sky coverage, and faster cadence than all previous γ-ray instruments. This transformative capability permits: (a) the accurate identification of the γ-ray emitting objects and correlations with observations taken at other wavelengths and with other messengers; (b) construction of new γ-ray maps of the Milky Way and other nearby galaxies where extended regions are distinguished from point sources; and (c) considerable serendipitous science of scarce events -- nearby neutron star mergers, for example. Advances in technology push the performance of new γ-ray instruments to address:
  • How do white dwarfs explode as Type Ia Supernovae (SNIa)?
  • What is the distribution of 56Ni production within a large population of SNIa?
  • How do SNIa γ-ray light curves and spectra correlate with their UV/optical/IR counterparts?
  • How do massive stars explode as core-collapse supernovae?
  • How are newly synthesized elements spread out within the Milky Way Galaxy?
  • How do the masses, spins, and radii of compact stellar remnants result from stellar evolution?
  • How do novae enrich the Galaxy in heavy elements?
  • What is the source that drives the morphology of our Galaxy's positron annihilation γ-rays?
  • How do neutron star mergers make most of the stable r-process isotopes?
Over the next decade, multi-messenger astronomy will probe the rich astrophysics of transient phenomena in the sky, including light curves and spectra from supernovae and interacting binaries, gravitational and electromagnetic signals from the mergers of compact objects, and neutrinos from the Sun, massive stars, and the cosmos. During this new era, the terrestrial Facility for Rare Isotope Beams (FRIB) and Argonne Tandem Linac Accelerator System (ATLAS) will enable unprecedented precision measurements of reaction rates with novel direct and indirect techniques to open perspectives on transient objects such as novae, x-ray bursts, kilonovae, and the rapid neutron capture process. This ongoing explosion of activity in multi-messenger astronomy powers theoretical and computational developments, in particular the evolution of community-driven, open-knowledge software instruments.

The unique information provided by MeV γ-ray astronomy to help address these frontiers makes now a compelling time for the astronomy community to strongly advocate for a new γ-ray mission to be operational in the 2020s and beyond.

Check out the full white paper submitted to the 2020 Decadal Survey.


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