How is gravitational microlensing used to discover exoplanets?
This video is from my Astrophysics for Beginners online course
Let’s say we want to discover whether a distant star has exoplanets orbiting around it. How can we do it? Well, if that star passes in front of a distant light source then that background light will bent by the star’s gravity and continue on towards Earth. It’s like the star is acting as a giant magnifying glass or lens. That’s why it’s called gravitational microlensing.
The effect of the lensing is that the light from the distant light source is magnified. Astronomers are used to seeing a smooth increase in brightness. But if the star has a planet orbiting around it then the planet also contributes to the lensing and so there’s an additional spike in the magnification.