Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B


The gravity wave event observed on August 17, 2017, and it implications for understanding of mechanisms for producing heavy elements

Mark Conde
Physics Department and Geophysical Institute



On October 16 it was announced that the LIGO/VIRGO gravitational wave detection collaborative had observed an event at 12:41:04 UTC on August 17 2017. The creatively-named "GW170817" event is now the fifth confirmed the gravity wave detection. Nevertheless, it is proving far more interesting than its predecessors. 1.7 seconds after GW170817, the NASA Fermi and ESA INTEGRAL satellites observed a gamma-ray burst which, in an extraordinary coincidence, was found to be named "GRB 170817A". Only 10.9 hours after the gravitational wave detection, the Swope Supernova Survey collaborative identified an optical counterpart (named SSS17a) located in the nearby elliptical galaxy NGC 4993. This galaxy is only 130 million light-years distant and was discovered within the constellation Hydra in 1789 by William Herschel. These near-coincident detections galvanized the astronomy community into an extraordinary global collaboration to observe and understand the event.
The resulting observations show that GW170817 was, by a factor of ~10, the closest gravity wave event yet observed, and also the "loudest". Unlike previous events, all of which originated from mergers of stellar remnant black holes with several tens of solar masses, this event was due to a merger between two inspiralling neutron stars, each of which were roughly in the range 1-2 solar masses. The event duration of ~30 seconds was also by far the longest yet seen. Previous events lasted less than a second.
The coordinated observations allow this event to place strong constraints on many aspects of astrophysics, cosmology, and fundamental physics; numerous fundamental new insights and discoveries are likely. Here, however, I will focus on mainly on one aspect - the implications of this event for our understanding of the processes by which certain heavy elements (such as gold and platinum) are formed. Indirect evidence has been mounting since the early 2000s to suggest that neutron star mergers may be the major generator of such elements - but it was not until GW170817 that we have had definitive evidence of the efficacy of this mechanism.


Friday, 3 November 2017

Globe Room, Elvey Building

3:45 PM