Gravitational Waves Observed

Earlier this week the Gravitational Wave Laboratories LIGO and VIRGO announced the first observation of gravitational waves from the merging of two neutron stars on August 17, 2017. The merging of two neutron stars has long been suggested as one of several possible sites that enrich our Universe in heavy elements such as gold and platinum via the so called rapid neutron capture process (r-process). The r-process is a primary research goal for NSCL and FRIB, where the extremely neutron rich rare isotopes that drive this process can be produced and studied. Indeed, immediate followup observations with traditional telescopes of the merger afterglow, a so called kilonova, show that heavy elements are produced and ejected. This is exciting news for NSCL and FRIB. The actual identification of an r-process site allows researchers to determine the important rare isotopes that need to be studied. “It marks the beginning of an era of analyzing direct r-process observations, for which FRIB is needed.” says Dan Kasen, astrophysicist at UC Berkeley who led model calculations interpreting the new observations.


This image captures phenomena observed following the neutron star merger known as GW170817. They include gravitational waves (pale arcs), a near-light-speed jet that produced gamma rays (magenta), expanding debris from a kilonova that produced ultraviolet (violet), optical and infrared (blue-white to red) emission, and, once the jet directed toward us expanded into our view from Earth, X-rays (blue). Credits: NASA's Goddard Space Flight Center/CI Lab


A neutron star is a very dense star that has the mass of about two Suns compressed into roughly the size of a large city (~10 miles). When two of these neutron stars get close together, they start to “dance” around each other, slowly getting closer and emitting energy in the form of gravitational waves that spread through space with the speed of light. Last August, three Gravitational Wave detectors spread around the Earth detected a signal, within a fraction of a second from each other, from the merger of two neutron stars. They quickly alerted other astronomical observatories and they all pointed in the same direction. These follow-up observations clearly indicate that indeed neutron star material is ejected in space, and that both light and heavy elements are produced. Finding out what exactly these elements are, how they were produced, and determining the conditions that lead to the production of the different elements will require rare isotope data from FRIB and advanced computer models. These rare isotopes live only for fractions of seconds and can therefore not be found naturally on earth to study their properties. The only way to study them is by producing them in rare isotope laboratories. Some of them can be produced at the NSCL today, but the vast majority is inaccessible right now, and only with FRIB will we be able to dive into their inner workings, and be able to connect the dots revealed in the new observations.