Greifswald Physics Colloquium: Dr. Smaranika Banerjee

We are made of, and surrounded by, elements such as oxygen, carbon, iron, and even gold, yet the question of where the heaviest elements, such as gold, come from remains one of the great mysteries in astrophysics. A leading theoretical hypothesis is that these heavy elements are produced in binary neutron star mergers. When two neutron stars collide, they eject neutron-rich matter in which heavy elements are formed through rapid neutron-capture nucleosynthesis, or the r-process. The radioactive decay of these newly synthesized elements powers a short-lived ultraviolet, optical, and infrared transient known as a kilonova, which can be observed with telescopes. At the same time, the merger produces gravitational waves detectable by ground-based observatories, making these systems powerful multi-messenger sources. The first joint detection of gravitational waves and a kilonova in 2017 confirmed neutron star mergers as sites of heavy-element production, but important questions remain: do they produce enough material to explain the heavy elements we observe, what can kilonova light curves and spectra reveal about the ejecta, and are additional cosmic sources needed? In this talk, I will introduce the broader context and importance of this field, discuss these open questions, and highlight recent progress in understanding kilonovae and neutron star mergers.