Kilonova

In a kilonova, two neutron stars merge. On 10/16/2017i, LIGO and Virgo announced the first detection of gravitational waves matched with visual data. The source was a kilonova in the galaxy NGC 4993 (constellation Hydra).

Image source: Heise, NSF/LIGO/Sonoma State University/A. Simonnet.
Recent Youtube animations and information: