The discovery was made by an international team of scientists led by Patrick Kelly (of the University of Minnesota), Jose Diego (of the Instituto de Física de Cantabria in Spain) and Steven Rodney (of the University of South Carolina). Together, they observed the distant star in the galaxy cluster MACS J1149-2223 in April 2016 while studying the supernova explosion known as heic1525 (aka. Refsdal).
“If dark matter is at least partially made up of comparatively low-mass black holes, as it was recently proposed, we should be able to see this in the light curve of LS1. Our observations do not favour the possibility that a high fraction of dark matter is made of these primordial black holes with about 30 times the mass of the Sun."