What observation characterizes Strong Lensing used in mass determination?

Answer

The severe distortion of background light resulting in multiple images or dramatic arcs.

Strong lensing occurs when the alignment is precise, causing the light of a background object to be severely magnified, duplicated, or smeared into recognizable arcs by the foreground galaxy's gravity.

What observation characterizes Strong Lensing used in mass determination?
measurementgalaxyastronomymethodmass