Artists impression of a neutron star merger
Artist’s impression of jets of material from first confirmed neutron star merger - Image copyright Mark Garlick/University of Warwick

 

2017 marks the beginning of multi-messenger astrophysics: for the first time ever the gravitational waves from the merger of two ultra-dense stars, so-called neutron stars, were detected. Directly after the burst, a flash of gamma-rays was observed from the same location and in the following weeks a firework all accross the electromagnetic spectrum was observed. This combined "multi-messenger observation" has lead to major leaps forward for various fields in physics. It showed that neutron star mergers produce gravitational waves as predicted by Einstein's Theory of Relativity, that gravitational waves travel at the speed of light and it allowed for a new measurement of the expansion rate of the Universe. These observations further showed that neutron star mergers produce the heaviest elements in the Universe, such as gold and platinum. For all of these reasons, this event was celebrated by the Science Magazine as "The Breakthrough of the year 2017".

There was, however, a scientific controversy, whether the observed flash of gamma-rays was really due to a "classical" gamma-ray burst. Such a burst produces its radiation in an ultra-relativistic, highly collimated outflow. The alternative suggestion is that the radiation comes from a more slowly moving cloud of material called a "cocoon", but the event would not have looked like a bright gamma-ray burst to any observer in the Universe. The new observations that will be published in a forthcoming Nature  Astronomy paper now find good indications that the gamma-radiation was indeed produced by the ultra-relativistic outflow and if we had seen this event from a different viewing angle, it would have looked like classical, very bright gamma-ray burst.

More information on this can be found here and the original nature paper can be found here: https://www.nature.com/articles/s41550-018-0511-3