Constraints on the Hubble constant from Supernova Refsdal's reappearance

Understand

The gravitationally lensed Supernova Refsdal appeared in multiple images, produced through gravitational lensing by a massive foreground galaxy cluster.

• After the supernova appeared in 2014, lens models of the galaxy cluster predicted an additional image of the supernova would appear in 2015, which was subsequently observed.
• We use the time delays between the images to perform a blinded measurement of the expansion rate of the Universe, quantified by the Hubble constant (H0).
• Using eight cluster lens models, we infer H0 = 64.8 +4.4-4.3 km / s / Mpc, where Mpc is the megaparsec.