Image credit: NSF/LIGO/Sonoma State University/A. Simonnet
Artist's Illustration of the merging of two neutron stars. Image credit: NSF/LIGO/Sonoma State University/A. Simonnet


Decisive contributions to the LIGO detector and the discovery of gravitational waves were the motivation for the choice of recipients for the Nobel Prize in Physics this year. Now the newest from this and other observatories : the first observations of gravitational waves from two merging neutron stars and, quickly thereafter, the identification of an optical counterpart in a nearby galaxy only 130 million light years away. This is the first time scientists have observed any phenomenon in both gravitational waves and electromagnetic radiation.

"At first I thought it was a regular supernova we were seeing. But soon we became aware that it was something more exciting", says Jesper Sollerman, astronomy professor at the Department of Astronomy, Stockholm University.

Around ten researchers from Oskar Klein Centre have participated in the study of this event. J. Sollerman, U. Feindt, A. Goobar, and S. Rosswog, from the departments of Physics and Astronomy at Stockholm University, are co-authors of an article on the electromagnetic counterpart to this merger event. The article is published today in the journal Science (Illuminating Gravitational Waves: A​ Concordant Picture of Photons from a Neutron Star Merger, Kasliwal et al. 2017.)



Co-author Stephan Rosswog is also involved in several other articles and leads his own study focusing on the production of heavy elements from these processes which he has modeled for many years now. "As far as I can see, my old predictions and calculations showing that the heaviest elements including gold, platinum and uranium are indeed formed in merging neutron stars seems to be confirmed by this finding. This is evidence that I have been waiting 20 years to see", says Stephan Rosswog.

With telescopes in Chile, OKC researchers J. Sollerman, C. Barbarino, M. Bulla, and F. Taddia, were able to follow how the optical light from the neutron star merger decreased and became more red as time passed after the event. These observations are now published in the journal Nature (A kilonova as the electromagnetic counterpart to a gravitational-wave source, Smartt et al. 2017).

Oskar Klein Centre scientists were also involved in the search for neutrinos from the merger of neutron stars although no neutrinos were detected from this event.

OKC scientists are involved in a number of new initiatives that seek to better identify and understand events which produce gravitational waves and electromagnetic radiation, including the Gravitational Radiation and Electromagnetic Transients research environment (GREAT). Soon researchers at the OKC and other scientists involved in the Zwicky Transient Facility collaboration will complete a new camera for use at Palomar Observatory in California. "This will be one of the most effective instruments for finding the optical counterparts to future neutron star mergers when LIGO and Virgo begin to observe again after the summer", says Jesper Sollerman.