Finding exoplanets with gravitational microlensing

Microlensing is a form of gravitational lensing. While Euclid mostly uses lensing to explore massive faraway objects, such as clusters of galaxies, this new image of the galactic centre helps scientists to study lenses on the smallest scales – caused by stars and exoplanets in our own galaxy.

Microlensing relies on the chance alignment of two stars with an observer. As one star crosses in front of another, the nearer star acts like a cosmic magnifying glass, bending and brightening the background star’s light. If a planet orbits the nearer star, its gravity also bends this light, in a slightly uneven way. This tiny additional change in brightness is how the presence of a planet is revealed.

“To catch microlensing, you need to observe parts of the sky that are crowded with stars, such as close to the centre of our galaxy,” explains Jean-Philippe Beaulieu of the Institut d’Astrophysique de Paris in France, and the University of Tasmania in Australia. Jean-Philippe was the original instigator of Euclid’s galactic bulge survey, and he co-led the exoplanet working group of the Euclid Consortium.

“During the last twenty years, almost 300 exoplanets have been discovered using this technique, all with ground-based telescopes and all towards the centre of our galaxy. This image from Euclid includes 51 known planetary systems – and it will assist in studying many more that will be found,” he adds.