March 04, 2026 | 3:30pm - 4:30pm
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03/04/2026 15:30
03/04/2026 16:30
University of Pennsylvania Physics & Astronomy Colloquium
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Topic: From Mergers to Magnetars: Quest for the Origin of the Heaviest Elements
Speakers: Brian David Metzger , Columbia University & Flatiron Institute
More: https://www.ias.edu/sns/events/university-pennsylvania-physics-astronomy-colloquium-27
Roughly half of the elements heavier than iron in the universe are
forged in extreme, neutron-rich environments where nuclei capture
neutrons faster than they can undergo beta decay—the so-called
r-process. The discovery of "kilonova" emission following the
gravitational wave event GW170817 established binary neutron star
mergers as an important r-process site, but several observations
suggest that additional sources may be required, particularly to
explain the abundances of low-metallicity stars.
In neutron star mergers, heavy elements form in outflows from the
accretion disk that feeds the newly formed black hole. Broadly similar
neutron-rich accretion flows are created in "collapsars"—the
explosions of massive, rotating stars. Particularly massive
collapsar disks can become gravitationally unstable and fragment,
forming swarms of low-mass neutron stars that coalesce via
gravitational waves hierarchically within the same disk environment,
potentially triggering a "multi messenger symphony". The recent
discovery of candidate sub-solar mass neutron star merger events by
LIGO/Virgo in association with supernovae may support this scenario.
A different pathway to heavy-element nucleosynthesis arises in the
giant flares from highly magnetized neutron stars (magnetars), where
crustal material can be ejected into space. I will present evidence,
in the form of a previously unexplained MeV gamma-ray signal, that the
famous Galactic magnetar giant flare from December 2004 synthesized
~1e-6 solar masses of r-process nuclei. Radioactive decay of these
ejecta also powers a very short-lived (~minutes) UV/optical
transient—a “mini-kilonova”, which could be detected following
extragalactic flares with upcoming missions such as ULTRASAT and
UVEX.
David Rittenhouse Laboratory Room A4, University of Pennsylvania
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