Detection of the Gravitational Lens Magnifying a Type Ia Supernova

Understand

Objects of known brightness, like Type Ia supernovae (SNIa), can be used to measure distances.

• If a massive object warps spacetime to form multiple images of a background SNIa, a direct test of cosmic expansion is also possible.
• However, these lensing events must first be distinguished from other rare phenomena.
• Recently, a supernova was found to shine much brighter than normal for its distance, which resulted in a debate: was it a new type of superluminous supernova or a normal SNIa magnified by a hidden gravitational lens? Here we report that a spectrum obtained after the supernova faded away shows the presence of a foreground galaxy--the first found to strongly magnify a SNIa.