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Gravitational lensing

How it works:

According to Einstein’s general theory of relativity, time and space are merged into one quantity called spacetime. Under this theory, massive objects cause space-time to bend, and gravity is simply the bending of space-time. When light moves through spacetime, the theory predicts that the path of light is also bent by the mass of an object. Gravitational lensing is an observable example of the application of Einstein’s theory.

Einstein ring:

This phenomenon was predicted by Albert Einstein already in 1915 in his General Theory of Relativity. The Einstein ring is a ring of electromagnetic radiation from a distant object, created by the gravitational effect of a galaxy in the foreground.

Credit: and

The orange galaxy in the center of the ring acts here as a gravitational lens.



Microlensing – a special type of gravitational lensing

The microlensing method finds planets by the effect of their gravity on light coming to Earth from a more distant background star. The brightness variations of the background star can be used to infer the existence of a planet, even if no light is measured directly from the planet or its central star.


Our SPP 1992 member Yiannis Tsapras held a talk about exoplanets and microlensing:

The first microlensing event:

In July 2003, the first exoplanet was found via microgravity lensing effect. OGLE-2003-BLG-235L is located in the constellation Sagittarius and orbits an orange dwarf star. Read more about it here.

Credit: and

Interesting questions on the topic:

Q: What parameter is obtained by microlensing?
A: From the measurements one can read the ratio between the mass of the planet and that of its star. Furthermore, one gets the separation between the planet and its host star at the time of the observation .

Q: What is the difference between gravitational lensing and microlensing?
A: Gravitational lensing is caused by a huge object like a galaxy. Microlensing is a special case of gravitational lensing where the lens is a star within our own galaxy

Recommended books to the topic:

Gravitational Lenses

P. Schneider, J. Ehlers, E. E. Falco

Publisher: Springer Verlag

ISBN: 9780387970707

Introduction to Gravitational Lensing: With Python Examples

Massimo Meneghetti

Publisher: Springer Verlag

ISBN: 978-3-030-73582-1

Find more books to the topic exoplanets and astronomy for children, amateurs and scientists in our booklist.

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