The Fermi Science Playoffs celebrate 10 years of the Fermi Gamma-ray Space Telescope's exploration of the high-energy universe. Surviving all early rounds of voting, these two finalists in the competion square off at last.

It is a candidate for the brightest and most powerful explosion ever seen -- what is it? The flaring spot of light was found by the All Sky Automated Survey for Supernovae (ASASSN) in June of last year and labelled ASASSN-15lh.