ASASSN-15lh

ASASSN-15lh is a supernova detected on 14 June 2015. It is the most luminous supernova ever detected. At its brightest it was 50 times brighter than the whole Milky Way.
The supernova is some 3.8 billion light-years from Earth. It was found by the All Sky Automated Survey for SuperNovae (ASAS-SN).