We knew from theoretical models that mergers of massive, gas-rich galaxies were more frequent in the past. Now we've found that these mergers are responsible for producing both the nearby obscured quasar population and their distant cousins.

If you know the shape of the lens and the image you get, you can work out the path that light followed between the object and your eye.

We cannot explain the phenomenon of gravitational lensing without general relativity, and this is where MOND spectacularly fails.

Priyamvada Natarajan Quotes