In gravitational microlensing, astronomers watch what happens when a massive object passes in front of a star from our perspective on Earth. The nearby object's gravitational field bends and magnifies the light from the distant star, acting like a lens.
This produces a light curve — a brightening and fading of the faraway star's light over time — whose characteristics tell astronomers a lot about the foreground object, which is often a star. If this star has any planets, these can generate secondary light curves, alerting researchers to their presence.
Gravitational microlensing is less biased toward planets that orbit relatively far from their stars than the transit or radial velocity methods. Researchers have even used it to find so-called "rogue planets," which cruise through the depths of space without a parent star.
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