Gravitational Lensing  – The Cosmic Magnifying Glass

What is it?

Light doesn’t always travel in straight lines in space. Due to Einstein’s Theory of General Relativity, space-time is warped by massive objects like stars and galaxies. This can cause light to bend around these massive objects, like how a telescope lens bends light. We call this Gravitational Lensing.

Uses of Lensing

This is an incredibly valuable tool for astrophysics.

Strong Lensing

This occurs when a massive object like a galaxy cluster is precisely aligned with a background source. It produces arcs, multiple images of the same object and Einstein rings (shown below).

This image shows an Einstein Ring viewed from the Hubble Telescope.

Weak Lensing

This causes slight distortions in the shapes of background galaxies. This can be used to map dark matter in the universe, which is what the ESA’s Euclid does.

Microlensing

This can be used to detect objects that emit little or no light such as exoplanets by measuring the apparent brightening of the source as the alignment of the lens and source change.

Example

An example of this which I found to be incredibly interesting was when a Supernova was seen three times hundreds of days apart. The image below shows three images of the same supernova hosting galaxy. Due to strong gravitational lensing, the same galaxy can be viewed ~320 and ~1000 days apart in the same image and appears roughly 20 times more magnified.

This observation from the NASA/ESA/CSA James Webb Space Telescope contains three different images of the same supernova-hosting galaxy.

Gravitational lensing is an incredibly powerful tool, and I am incredibly excited to see what more interesting discoveries it can yield.

Sources

[1]https://upload.wikimedia.org/wikipedia/commons/1/11/A_Horseshoe_Einstein_Ring_from_Hubble.JPG

[2] https://esawebb.org/images/potm2302b/

[3]https://www.esa.int/ESA_Multimedia/Videos/2024/09/Weak_gravitational_lensing_how_Euclid_maps_dark_matter

[4]https://science.nasa.gov/missions/hubble/nasas-hubble-discovers-four-images-of-same-supernova-split-by-cosmic-lens/

[5] https://www.space.com/gravitational-lensing-explained