Brian Metzger, Associate Professor of Physics, Columbia University
The astrophysical site(s) giving rise to the creation of the heaviest elements in the Universe, those produced by the rapid capture of neutrons onto lighter seed nuclei (the "r-process"), has remained a long-standing mystery since the seminal work of Burbidge, Burbidge, Hoyle & Fowler (1957). On August 17 of last year, the LIGO gravitational wave observatory detected the first binary neutron star merger event (GW170817), a discovery followed by the most ambitious electromagnetic (EM) follow-up campaign ever conducted. Within two seconds of the merger, a weak burst of gamma-rays was discovered by the Fermi and INTEGRAL satellites. Within 11 hours, a bright but rapidly-fading thermal optical counterpart was discovered in the galaxy NGC 4993 at a distance of only 130 million light years. The properties of the optical transient match well predictions for "kilonova" (a.k.a. "macronova") emission powered by the radioactive decay of heavy nuclei synthesized by the r-process in the expanding neutron-rich merger ejecta. The spectral evolution of the thermal signal to near-infrared wavelengths demonstrates that the inner, slower portions of the ejecta contain heavy lanthanide nuclei. I will describe efforts to interpret the EM counterparts of GW170817, and the resulting implications for the origin of the r-process and the unknown properties of neutron stars, couched within the historical context of theoretical and nuclear experimental work, much of it done at Caltech. Time permitting, I will preview some of the diversity predicted for the kilonova emission in the impending era of multi-messenger astronomy, once Advanced LIGO/Virgo reach design sensitivity and detect a neutron star merger as frequently as once per week.
The Lauritsen Memorial Lecture commemorates two former professors of physics at Caltech: Charles C. Lauritsen and Thomas Lauritsen. Together they served the Institute for more than 68 years, and their commitment to excellence played a significant role in Caltech's development and accomplishments.